▶️ Answer/Explanation
When a purple crystal (such as potassium manganate(VII)) is dropped into water, two processes occur simultaneously: first, the crystal dissolves in the water as the water molecules interact with and break apart the ionic lattice, releasing coloured ions into solution — this is dissolution. Second, once the ions are free in solution, they spread out from the region of high concentration (near the crystal) to regions of lower concentration throughout the water — this is diffusion, explained by kinetic particle theory as the random movement of particles. Both dissolution and diffusion are therefore taking place, and no chemical reaction occurs since the process is entirely physical. This combination of dissolving followed by diffusion of the coloured ions accounts for the spreading purple colour observed in the diagram.
✅ Answer: D
✅ Answer: D
▶️ Answer/Explanation
An element consists of only one type of atom (identified by its proton number), and it cannot be broken down into simpler substances by chemical means. A compound contains two or more different elements chemically bonded together in fixed proportions, and its properties differ from those of its constituent elements; it can only be separated by chemical reactions. A mixture, by contrast, contains two or more substances that are not chemically combined — the components retain their individual properties and can be separated by physical means such as filtration, distillation or chromatography. Row C correctly reflects all three of these definitions without contradiction, making it the only fully accurate row in the table.
✅ Answer: C
✅ Answer: C
▶️ Answer/Explanation
An electron carries a relative charge of –1, equal in magnitude but opposite in sign to that of a proton (+1), which is why atoms are electrically neutral when the number of protons equals the number of electrons. The relative mass of an electron is approximately 1/1840 of that of a proton or neutron, which is so negligibly small that it is considered to be effectively zero (or 1/2000) for most calculations at this level. Protons and neutrons each have a relative mass of 1 and are located in the nucleus, while electrons occupy shells surrounding the nucleus and contribute virtually nothing to the overall mass of the atom. Therefore, the correct answer assigns a relative charge of –1 and a relative mass of 0 (or negligible) to the electron.
✅ Answer: D
✅ Answer: D
▶️ Answer/Explanation
Isotopes are defined as atoms of the same element that have the same number of protons (same atomic number) but different numbers of neutrons (different mass numbers); the number of protons determines which element an atom belongs to. To identify isotopes, you must look for two particles with identical proton numbers but differing neutron counts — any difference in proton number means the particles belong to entirely different elements and cannot be isotopes. From the diagram, particles W and Y have the same number of protons but different numbers of neutrons, satisfying the definition of isotopes exactly, while the other pairs either differ in proton number or have identical nucleon compositions. Therefore, W and Y are isotopes of the same element.
✅ Answer: B
✅ Answer: B
▶️ Answer/Explanation
Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions arranged in a giant ionic lattice, which requires a large amount of energy to overcome — this gives them characteristically high melting points. When solid, the ions are fixed in their lattice positions and cannot move freely, so ionic compounds do not conduct electricity in the solid state; however, when melted or dissolved in water, the ions become free to move and carry charge, making them good electrical conductors in the molten or aqueous state. Any row suggesting low melting points or conductivity in the solid state would be incorrect. Row D correctly combines a high melting point with poor electrical conductivity when solid and good conductivity when molten or in solution.
✅ Answer: D
✅ Answer: D
▶️ Answer/Explanation
Methane (CH4) is formed when one carbon atom shares electrons with four hydrogen atoms through single covalent bonds. Carbon has 4 electrons in its outer shell and needs 4 more to achieve a full outer shell of 8 (noble gas configuration), while each hydrogen atom has 1 electron and needs 1 more to achieve a full outer shell of 2; by sharing one pair of electrons in each of the four C–H bonds, both carbon and all four hydrogen atoms simultaneously achieve stable noble gas electronic configurations. Each single covalent bond therefore consists of exactly one shared pair of electrons — giving carbon 4 bonds and each hydrogen 1 bond. Row A correctly identifies that 4 single covalent bonds are formed, each consisting of one shared pair of electrons, with the carbon atom achieving a full outer shell of 8 electrons.
✅ Answer: A
✅ Answer: A
▶️ Answer/Explanation
In a neutralisation reaction between sodium hydroxide and nitric acid, both reactants are used as aqueous solutions in the laboratory, so their state symbols must be (aq) — options C and D are immediately eliminated because they incorrectly show both reactants as liquids (l), which would imply pure molten substances rather than aqueous solutions. The product sodium nitrate (NaNO3) is a soluble salt that remains dissolved in the aqueous solution at room temperature, so its correct state symbol is (aq), not (l) — this eliminates option B which incorrectly assigns (l) to NaNO3. Water produced in the reaction is in the liquid state (l), and option A correctly assigns all state symbols, making it the only fully accurate equation.
✅ Answer: A
✅ Answer: A
▶️ Answer/Explanation
The relative formula mass is calculated by summing the relative atomic masses of all atoms present in the formula NH4NO3. Using standard relative atomic masses — N = 14, H = 1, O = 16 — the calculation is as follows: there are 2 nitrogen atoms (2 × 14 = 28), 4 hydrogen atoms (4 × 1 = 4), and 3 oxygen atoms (3 × 16 = 48), giving a total of 28 + 4 + 48 = 80. Options B, C and D are all incorrect as they result from either using wrong atomic masses or miscounting the number of atoms of each element in the formula. Therefore, the relative formula mass of ammonium nitrate is 80.
✅ Answer: A
✅ Answer: A
▶️ Answer/Explanation
During the electrolysis of concentrated aqueous sodium chloride, the solution contains Na+, Cl–, H+ and OH– ions. At the cathode (negative electrode), hydrogen gas is preferentially discharged as H+ ions are attracted to the negative electrode and gain electrons (2H+ + 2e– → H2); sodium ions are not discharged because sodium is too reactive. At the anode (positive electrode), chloride ions are preferentially discharged in concentrated solution to produce chlorine gas (2Cl– → Cl2 + 2e–), rather than OH– ions which would be preferentially discharged in dilute solution. Therefore, gas X produced at the anode is chlorine and gas Y produced at the cathode is hydrogen.
✅ Answer: B
✅ Answer: B
▶️ Answer/Explanation
A hydrogen–oxygen fuel cell operates by combining hydrogen and oxygen to generate electricity, with water (H2O) as the only chemical product — since no carbon-containing fuel is burned, no carbon dioxide is produced at all, making option A correct and one of the key environmental advantages of fuel cells over petrol engines. Option B is incorrect because oxygen is an essential reactant in the fuel cell; without it, the electrochemical reaction cannot take place. Option C is incorrect because the only waste product is water, which is neither acidic nor a gas under normal operating conditions. Option D is incorrect because the overall reaction (hydrogen + oxygen → water) is exothermic, releasing energy that is converted into electrical energy.
✅ Answer: A
✅ Answer: A
▶️ Answer/Explanation
In a reaction pathway diagram, the relative energy levels of the reactants and products determine whether the reaction is exothermic or endothermic. When the products are at a higher energy level than the reactants, the reaction requires a net input of thermal energy from the surroundings — this is the definition of an endothermic reaction, and the enthalpy change ΔH is positive. Options C and D describe exothermic behaviour (energy released to surroundings, temperature of surroundings increases), which would only apply if the products were at a lower energy level than the reactants. Option A is unrelated to the reaction pathway diagram, as reaction rate is not shown or implied by energy level diagrams. Since the diagram shows products higher in energy than reactants, the reaction is endothermic, making option B correct.
✅ Answer: B
✅ Answer: B
▶️ Answer/Explanation
The rate of a reaction depends on the frequency of successful collisions between reactant particles. Increasing the size of lumps of calcium carbonate reduces the total surface area exposed to the acid — with less surface area available, fewer acid particles can collide with the solid at any given time, resulting in a lower frequency of collisions and therefore a decreased rate of reaction. Options A and D would both increase the rate: higher acid concentration means more acid particles per unit volume (more frequent collisions), and higher temperature gives particles more kinetic energy (more frequent and more energetic collisions). Option B, increasing the volume of acid at the same concentration, does not affect the rate as it does not change the concentration or surface area. Therefore, only increasing the lump size decreases the rate.
✅ Answer: C
✅ Answer: C
▶️ Answer/Explanation
Hydrated copper(II) sulfate (CuSO4•5H2O) is the blue form, as the water of crystallisation chemically combined within its crystal lattice gives it the characteristic blue colour. When hydrated copper(II) sulfate is heated, the water of crystallisation is driven off, converting it to anhydrous copper(II) sulfate (CuSO4), which is white — this is the forward reaction in the reversible equation shown. The reverse reaction (white → blue) is brought about simply by adding water to the anhydrous form, which rehydrates the crystals and restores the blue colour. Therefore, the blue form is hydrated copper(II) sulfate and the change to the white anhydrous form is brought about by heating.
✅ Answer: D
✅ Answer: D
▶️ Answer/Explanation
In redox reactions, oxidation and reduction always occur simultaneously — a substance that loses oxygen or electrons is oxidised (and acts as a reducing agent), while a substance that gains oxygen or electrons is reduced (and acts as an oxidising agent). To evaluate each statement, the changes in oxygen content or oxidation numbers of each species in the equations must be carefully tracked: a species gaining oxygen is being oxidised, and a species losing oxygen is being reduced. Statements 1 and 3 correctly identify which species is oxidised and which is reduced in their respective equations, correctly applying the definitions of oxidation (gain of oxygen/loss of electrons) and reduction (loss of oxygen/gain of electrons). Statements 2 and 4 incorrectly assign the roles of oxidation and reduction, either by misidentifying the oxidising or reducing agent or by reversing the direction of electron/oxygen transfer.
✅ Answer: B
✅ Answer: B
▶️ Answer/Explanation
Each indicator has a specific and well-defined colour change depending on whether the solution is acidic or alkaline. Litmus turns blue in alkaline solution (not yellow), and thymolphthalein turns pink/violet in alkaline solution (it is colourless in acid and pink in alkali). Universal indicator turns purple/violet at pH 14, not yellow. Methyl orange, however, turns yellow in alkaline conditions — it is red in strongly acidic solutions, orange near neutral, and yellow in alkaline solutions — making it the only indicator from the list that produces a yellow colour at pH 14. Therefore, methyl orange is the correct answer.
✅ Answer: B
✅ Answer: B
▶️ Answer/Explanation
Acidic oxides are formed from non-metals and dissolve in water to produce acidic solutions or react with bases to form a salt and water — examples include SO2, SO3, CO2 and NO2. Basic oxides are formed from metals and react with acids to form a salt and water — examples include CuO, CaO, MgO and Fe2O3. Any row containing a metallic oxide in the acidic column or a non-metallic oxide in the basic column would be incorrect. Row C correctly pairs a non-metal oxide (acidic) with a metal oxide (basic), satisfying both definitions simultaneously without confusion with amphoteric oxides such as Al2O3 or ZnO, which can react with both acids and bases.
✅ Answer: C
✅ Answer: C
▶️ Answer/Explanation
When excess copper(II) carbonate is added to hydrochloric acid, the reaction produces aqueous copper(II) chloride, water and carbon dioxide; the key word here is excess — this means not all the copper(II) carbonate has reacted, so there is unreacted solid copper(II) carbonate remaining in the mixture alongside the copper(II) chloride solution. The immediate next step must therefore be filtration to remove this excess unreacted solid carbonate from the solution, leaving behind a pure aqueous copper(II) chloride filtrate. Only after filtration can crystallisation be carried out to obtain solid copper(II) chloride crystals from the solution. Titration is irrelevant here as it is used for acid-alkali reactions, and simply evaporating without filtering first would leave impurities in the product.
✅ Answer: C
✅ Answer: C
▶️ Answer/Explanation
Across any period of the Periodic Table, metallic character decreases from left to right as the nuclear charge increases, pulling electrons more strongly and making it harder for atoms to lose electrons. Therefore, an element further to the left in the same period is always more metallic than one to its right. Statement 2 is correct because beryllium (Group II) is to the left of carbon (Group IV) in Period 2, making beryllium more metallic. Statement 4 is correct because magnesium (Group II) is to the left of silicon (Group IV) in Period 3, making magnesium more metallic. Statements 1 and 3 are both incorrect — sodium (Group I) is more metallic than aluminium (Group III), and lithium (Group I) is more metallic than boron (Group III), not the other way around.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
As Group I is descended from lithium to caesium, three key trends are observed. The melting point decreases because the metallic bonds become weaker as the atomic radius increases and the delocalised electrons are further from the nucleus. The density increases because each successive element has a significantly heavier nucleus even though the atomic size also grows, resulting in a net increase in mass per unit volume. The reactivity increases because the outer electron is further from the nucleus and more shielded by inner electron shells, making it increasingly easy to lose that electron and form a positive ion. This gives a combination of decreasing melting point, increasing density, and increasing reactivity.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Chlorine and bromine are both members of Group VII (halogens) and share the similarity of existing as diatomic molecules (Cl₂ and Br₂), meaning both are composed of pairs of atoms bonded covalently. However, they differ in their physical state at room temperature and pressure (r.t.p.): chlorine is a pale yellow-green gas while bromine is a red-brown liquid, reflecting the increase in intermolecular forces down the group as the molecules become larger and have more electrons. Additionally, chlorine is more reactive than bromine, as the ability to gain an electron decreases down the group due to the increased atomic radius and greater electron shielding. Row D correctly identifies that both are diatomic (similarity) while differing in their states at r.t.p.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Transition elements are a block of metals found in the centre of the Periodic Table between Groups II and III, and they share a distinct set of physical and chemical properties. They are characterised by having high densities due to their tightly packed atomic structures and relatively large atomic masses, which makes them significantly denser than Group I and Group II metals. They also have high melting points because the metallic bonding in transition metals is very strong, involving multiple delocalised electrons per atom, resulting in metals such as iron, chromium and nickel requiring very high temperatures to melt. Other key properties include forming coloured compounds and commonly acting as catalysts, but the physical properties of high density and high melting point are the defining characteristics tested here.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Noble gases belong to Group VIII of the Periodic Table and are characterised by having a completely full outer electron shell, which makes them exceptionally stable and chemically unreactive. For a noble gas to be identified from an electronic structure diagram, its outermost shell must be completely filled — the first shell holds a maximum of 2 electrons, and subsequent shells hold a maximum of 8 electrons. Diagram A shows the electronic configuration 2, 8, 8, which corresponds to argon (proton number 18), a noble gas with a full outer shell of 8 electrons. The other diagrams show configurations with incomplete outer shells, meaning those atoms would need to gain, lose, or share electrons to become stable, which is characteristic of non-noble gas elements.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
When a metal that is above hydrogen in the reactivity series is added to a dilute acid, the metal displaces hydrogen from the acid, producing a salt and hydrogen gas. Zinc is positioned above hydrogen in the reactivity series, so it reacts with dilute hydrochloric acid according to the equation: Zn + 2HCl → ZnCl₂ + H₂. The hydrogen gas produced can be confirmed using the lighted splint test, which produces a characteristic squeaky pop. Carbon dioxide would only be produced if a carbonate reacted with an acid, chlorine is not released as it remains bonded in the zinc chloride salt, and oxygen is not a product of metal-acid reactions.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Aluminium is the metal of choice in aircraft manufacture primarily because of its remarkably low density of approximately 2.7 g/cm³, which is roughly one-third the density of iron or steel, allowing aircraft to be built with a much lighter structure and thereby improving fuel efficiency. In addition to its low density, aluminium also offers good resistance to corrosion due to the formation of a protective oxide layer on its surface, making it well suited to the demanding conditions of flight. Copper is too dense and is mainly used in electrical wiring due to its excellent conductivity; iron is far too heavy and prone to rusting; and potassium is far too reactive with moisture and air to be used as a structural metal in any application.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
The diagram shows a giant lattice structure where particles are arranged in a regular, repeating three-dimensional pattern — this is characteristic of giant structures, which include ionic lattices, giant covalent structures, and metallic lattices. Diamond is a giant covalent structure where each carbon atom is covalently bonded to four others in a tetrahedral arrangement forming an extensive lattice, and silicon(IV) oxide (SiO₂) similarly forms a giant covalent lattice structure with a comparable appearance. Simple molecular solids such as iodine do not form giant lattices — they consist of discrete molecules held together by weak intermolecular forces — and sodium chloride, while also a giant lattice, is ionic rather than covalent. Row B correctly identifies diamond and silicon(IV) oxide as the two solids represented by this type of giant covalent lattice diagram.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Solid P must satisfy two conditions simultaneously: it reacts with dilute acids and it conducts electricity in the solid state. Metals fulfil both criteria — they react with dilute acids (provided they are above hydrogen in the reactivity series) and they conduct electricity in the solid state due to the presence of delocalised electrons in their giant metallic lattice. Student Y correctly identifies P as a metal, which is the only category of solid that satisfies both properties. Student X suggesting an ionic compound is incorrect because ionic compounds do not conduct electricity in the solid state (ions are fixed in the lattice) and generally do not react with dilute acids in the same way. Student Z suggesting graphite is incorrect because although graphite does conduct electricity, it does not react with dilute acids. Therefore, only Student Y is correct.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Rusting is the specific corrosion of iron and steel, producing hydrated iron(III) oxide (Fe₂O₃·xH₂O), and it requires both oxygen and water to be present simultaneously — neither substance alone is sufficient to cause rusting. This has been demonstrated experimentally: iron nails placed in dry oxygen do not rust, and iron nails placed in boiled (oxygen-free) water sealed with oil also do not rust, but nails exposed to both oxygen and water rust readily. Carbon dioxide is not a required condition for rusting, although it can accelerate the process slightly by making water slightly acidic; it is not one of the two essential substances. Therefore, the correct answer identifies oxygen and water as the two necessary conditions for rusting to occur.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
The method used to extract a metal from its ore is directly linked to its position in the reactivity series. Highly reactive metals such as aluminium (above carbon in the reactivity series) cannot be reduced by carbon or carbon monoxide, so they must be extracted by the more energy-intensive process of electrolysis of their molten ores. Metals of moderate reactivity such as iron (below carbon but above hydrogen) can be extracted by reduction with carbon or carbon monoxide in a blast furnace. Metals of low reactivity such as copper (below hydrogen in the reactivity series) can be extracted by reduction with carbon, or in some cases found native; copper is also increasingly obtained by electrolytic refining. Row D correctly matches aluminium with electrolysis, iron with reduction by carbon/carbon monoxide, and copper with reduction or electrolysis, consistent with their positions in the reactivity series.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Domestic water treatment involves several distinct processes, each with a specific purpose. Sedimentation and filtration are used to remove suspended solid particles from the water, making it clear. Activated carbon (charcoal) is used to remove unpleasant tastes and odours from the water by adsorbing the organic compounds responsible for them — it does not kill microbes or remove solids effectively. Chlorination involves adding small amounts of chlorine to the water specifically to kill harmful microbes and bacteria, making the water safe to drink. Row B correctly pairs chlorination with the reason of killing microbes, which is the sole purpose of this treatment step and matches precisely with the syllabus requirement.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
An NPK fertiliser must supply all three essential elements for plant growth: nitrogen (N), phosphorus (P), and potassium (K). Ammonium sulfate provides nitrogen (from the ammonium ion, NH₄⁺), and potassium phosphate provides both phosphorus (from the phosphate ion, PO₄³⁻) and potassium (K⁺) — together these two compounds supply all three required elements N, P, and K. Option B is incorrect because calcium hydroxide is not a fertiliser and contains no N, P, or K in useful form. Option C lacks nitrogen entirely. Option D provides nitrogen and potassium but no phosphorus, so it cannot be classified as a complete NPK fertiliser. Therefore, only option A supplies all three elements N, P, and K when the two compounds are combined.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Each clue must be matched carefully against all four options. Clean, dry air is composed of approximately 78% nitrogen, 21% oxygen, and the remainder being noble gases and carbon dioxide — this immediately eliminates carbon dioxide (option A) as gas X, since CO₂ is present in clean air. Carbon monoxide (option B) and nitrogen dioxide (option D) are both eliminated because they are well-known causes of respiratory problems. Methane (CH₄) satisfies all three criteria: it is not a component of clean, dry air (it is produced by decomposition of vegetation and animal digestion), it does not cause respiratory problems, and it is a potent greenhouse gas responsible for contributing to global warming and climate change by absorbing and re-emitting thermal energy in the atmosphere.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Examining each statement against the displayed structure of the vitamin A fragment: Statement 1 is incorrect because the structure clearly contains carbon–carbon double bonds (C=C), which means it is unsaturated, not saturated — a saturated compound would have only single C–C bonds throughout. Statement 2 is correct because the structure shows two C=C double bonds, which are the defining functional group of alkenes, making this part of the molecule contain two alkene groups. Statement 3 is incorrect because a carboxylic acid requires the –COOH functional group (a carbonyl and hydroxyl on the same carbon), which is not present in this portion of the vitamin A structure. Therefore, only statement 2 is correct.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
In the fractional distillation of petroleum, the fractionating column operates on the principle that hydrocarbons with longer carbon chains have stronger intermolecular forces, higher boiling points, and therefore condense at higher temperatures lower down the column. As a result, fractions collected at the bottom of the column contain hydrocarbons with the longest chain lengths and highest boiling points, such as bitumen and fuel oil, while fractions collected at the top have the shortest chains, lowest boiling points, and highest volatility, such as refinery gases. Fraction D, being collected at the bottom of the fractionating column shown in the diagram, therefore contains the hydrocarbons with the longest carbon chain lengths.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Cracking is the thermal decomposition of larger, less useful alkane molecules into smaller, more useful molecules using high temperature and a catalyst; it always starts with a larger alkane as the reactant and produces at least one alkene among the products. Option A shows polymerisation (small alkenes joining to form a larger molecule), which is the reverse process. Option B shows hydrogenation, where an alkene reacts with hydrogen to form an alkane. Option C shows complete decomposition into carbon and hydrogen, which is not cracking. Option D correctly shows the cracking of hexane (C₆H₁₄, a larger alkane) breaking down into ethene (C₂H₄, an alkene) and butane (C₄H₁₀, a smaller alkane), which is precisely what cracking produces — a smaller alkane and an alkene.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Evaluating each statement carefully: Statement 1 is correct — ethanol is manufactured industrially by the catalytic addition of steam to ethene at 300°C and 6000 kPa in the presence of an acid catalyst. Statement 2 is incorrect — fermentation occurs at a much lower temperature of 25–35°C using yeast in the absence of oxygen; 55°C would denature the yeast enzymes and prevent fermentation. Statement 3 is correct — ethanol is a fuel that undergoes complete combustion to produce carbon dioxide and water, represented by C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O. Statement 4 is incorrect — ethanol (C₂H₅OH) is a saturated alcohol containing only single carbon–carbon bonds; it is ethene that contains the carbon–carbon double bond. Therefore, statements 1 and 3 are correct.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Ethanoic acid (CH₃COOH) behaves as a typical acid in its reactions, and the key here is identifying which reactions produce a gas. Magnesium (substance 1) reacts with ethanoic acid to produce magnesium ethanoate and hydrogen gas (Mg + 2CH₃COOH → (CH₃COO)₂Mg + H₂), so a gas is produced. Magnesium carbonate (substance 2) reacts with ethanoic acid to produce magnesium ethanoate, water, and carbon dioxide gas (MgCO₃ + 2CH₃COOH → (CH₃COO)₂Mg + H₂O + CO₂), so a gas is also produced. Magnesium oxide (substance 3) is a base that reacts with ethanoic acid in a neutralisation reaction to produce magnesium ethanoate and water only (MgO + 2CH₃COOH → (CH₃COO)₂Mg + H₂O) — no gas is evolved. Therefore, only substances 1 and 2 produce a gas.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Reaction R involves 2000 small molecules of ethene (CH₂=CH₂) joining together to form a single large molecule X with no other products — this is the definition of addition polymerisation, where the C=C double bonds open up and the molecules link together in a chain. CH₂=CH₂ is ethene, which is the starting small molecule used to build the polymer, making it the monomer. Since only one product (X) is formed and no other substance is released, this confirms it is addition polymerisation rather than condensation polymerisation. The product X is poly(ethene), which is a large molecule made of many repeating ethene units joined together, making it a polymer. Row A correctly identifies reaction R as addition polymerisation, CH₂=CH₂ as the monomer, and X as the polymer.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
A titration requires two key pieces of volumetric glassware that allow precise measurement of liquid volumes. A burette (piece 2) is essential as it allows the controlled, measured addition of one solution (the titrant) drop by drop into the other solution, with readings taken before and after to determine the exact volume added. A volumetric pipette (piece 4) is used to deliver a precise, fixed volume of the other solution into the conical flask before the titration begins, ensuring accuracy and reproducibility. A measuring cylinder (piece 1) is not precise enough for titration work, and a beaker (piece 3) cannot deliver or measure accurate volumes of solution. Together, the burette and volumetric pipette are the two essential pieces of equipment for performing an accurate acid-base titration.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Sea water is essentially a solution of dissolved salts (mainly sodium chloride) in water, and to obtain pure drinking water from it, the water must be separated from the dissolved salts. Distillation is the correct process — the sea water is heated until the water evaporates, the steam is then collected and condensed back into liquid pure water, leaving the dissolved salts behind in the original container. Crystallisation would be used to recover the dissolved salt, not the water. Filtration only removes insoluble solid particles and cannot separate dissolved salts from water. Chlorination is a water treatment step used to kill microbes but does not remove dissolved salts or purify sea water into drinking water. Therefore, distillation is the only process capable of separating water from dissolved salts in sea water.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
The two test results must be used together to identify X. The first test shows that adding dilute acid to X produces a gas that turns limewater milky, which is the confirmatory test for carbon dioxide — this means X contains the carbonate ion (CO₃²⁻), eliminating options B (aluminium nitrate) and D (ammonium nitrate) which contain no carbonate. The second test shows that adding aqueous sodium hydroxide to X and warming produces a gas that turns damp red litmus paper blue, which is the confirmatory test for ammonia — this means X contains the ammonium ion (NH₄⁺), eliminating option A (aluminium carbonate). Ammonium carbonate ((NH₄)₂CO₃) contains both the ammonium ion and the carbonate ion, satisfying both test results perfectly, and it is indeed a white solid.
✅ Answer: (C)
✅ Answer: (C)