▶️ Answer/Explanation
The diagram shows particles moving from a closely packed, ordered solid arrangement → a less ordered liquid arrangement → a widely spaced, random gas arrangement. Process X converts solid to liquid, which is melting. Process Y converts liquid to gas, which is boiling (or evaporating). Process Z converts solid directly to gas, bypassing the liquid state entirely, which is sublimation. Therefore, X = melting, Y = boiling, Z = sublimation, which corresponds to option D.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
A pure compound is a substance made of two or more elements chemically combined in fixed proportions throughout. Air is a mixture of gases (mainly nitrogen and oxygen), brass is an alloy (a mixture of copper and zinc), and petroleum is a mixture of hydrocarbons. Ethanol (C₂H₅OH) is a single chemical substance made of carbon, hydrogen and oxygen atoms bonded together in a definite ratio, making it a pure compound with a fixed boiling point and composition.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
In ionic bond formation, the Group I metal (potassium) loses its single outer-shell electron to achieve a stable noble gas configuration, forming a positively charged cation K⁺. The Group VII non-metal (fluorine) gains that one electron to complete its outer shell, forming a negatively charged anion F⁻. Metals always form positive ions by losing electrons, while non-metals form negative ions by gaining electrons — so options involving K⁻ or F⁺ are impossible under normal ionic bonding.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
The symbol \({ }_3^7\mathrm{Li}\) tells us the atomic (proton) number is 3 and the mass number is 7. Since the atom is neutral, the number of electrons equals the number of protons, which is 3. Electrons fill shells in order: the first shell holds a maximum of 2 electrons, and the remaining 1 electron occupies the second shell. Therefore the electronic configuration of lithium is 2, 1 — two electrons in the first shell and one electron in the second shell. The mass number of 7 is irrelevant to electron arrangement; it only tells us the total number of protons and neutrons in the nucleus.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Fluorine is in Group VII, meaning each fluorine atom has 7 outer-shell electrons. When two fluorine atoms bond, each contributes 1 electron to form a single shared covalent bond (one bonding pair), leaving 3 lone pairs on each fluorine atom. The correct dot-and-cross diagram must therefore show one shared pair of electrons between the two F atoms and exactly 3 lone pairs around each atom, giving each fluorine a complete outer shell of 8 electrons — the same configuration as the noble gas neon. Any diagram showing more than one shared pair or an incorrect number of lone pairs is wrong.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Graphite has a layered structure in which each carbon atom is covalently bonded to three others in flat hexagonal sheets. The layers are held together only by weak intermolecular forces, which allows them to slide over one another easily. This slippery, low-friction property is precisely what makes graphite an effective lubricant. Its use as an electrode relies instead on its ability to conduct electricity (due to delocalised electrons), not on its sliding layers; cutting tools and jewellery are properties associated with diamond, not graphite.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Checking each equation by counting atoms on both sides: Equation 1 (Fe₂O₃ + 3CO → 2Fe + 3CO₂) — Fe: 2=2, O: 3+3=6 and 6 ✓, C: 3=3 ✓ — balanced. Equation 2 (ZnCO₃ + 2HCl → ZnCl₂ + CO₂ + 2H₂O) — H: 2 left, 4 right ✗ — not balanced (should be H₂O not 2H₂O, i.e., only 1 H₂O). Equation 3 (Mg(NO₃)₂ + NaOH → Mg(OH)₂ + 2NaNO₃) — Na: 1 left, 2 right ✗ — not balanced. Equation 4 (CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂) — Ca:1=1, C:1=1, O:7=7, H:2=2, S:1=1 ✓ — balanced. Therefore equations 1 and 4 are correctly balanced.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
From the balanced equation, 1 mole of CH₄ produces 2 moles of H₂O. The molar mass of CH₄ is 12 + 4 = 16 g/mol, and the molar mass of H₂O is 2 + 16 = 18 g/mol. So 1 mole (16 g) of methane produces 2 moles (2 × 18 = 36 g) of water. Since 36 g of water is exactly 2 moles, only 1 mole (16 g) of methane is required. The ratio of masses is therefore CH₄ : H₂O = 16 g : 36 g, confirming that 36 g of water is produced from 16 g of methane.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
During the electrolysis of concentrated aqueous sodium chloride (brine), chloride ions (Cl⁻) are preferentially discharged at the anode producing chlorine gas, while hydrogen ions from water are discharged at the cathode producing hydrogen gas. During the electrolysis of dilute sulfuric acid, water molecules are effectively electrolysed: hydrogen gas is produced at the cathode (reduction of H⁺ ions) and oxygen gas is produced at the anode (oxidation of OH⁻/water). Therefore, for concentrated NaCl the products are chlorine at the anode and hydrogen at the cathode, and for dilute H₂SO₄ the products are oxygen at the anode and hydrogen at the cathode.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
A hydrogen-oxygen fuel cell converts chemical energy directly into electrical energy through the reaction of hydrogen and oxygen, with water as the only chemical product — making it a clean energy source. This electricity then powers an electric motor to drive the car. Option A is incorrect because it is electricity, not heat, that powers the car. Option B is incorrect because hydrogen is not present in air in usable quantities and must be stored separately. Option C is incorrect because the only emission is water vapour, not nitrogen gas.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
In a reaction pathway diagram, the relative energy levels of 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 energy from the surroundings — this is an endothermic reaction. Because the reaction absorbs thermal energy from the surroundings, the temperature of the surroundings decreases. This rules out statements 1 and 3, which describe an exothermic reaction where products are at a lower energy level than reactants and heat is released to the surroundings.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
A chemical change involves the formation of new substances with different chemical properties and is generally irreversible. When sodium is added to water, a vigorous reaction occurs producing sodium hydroxide and hydrogen gas (2Na + 2H₂O → 2NaOH + H₂), with observable evidence such as fizzing, heat production and the sodium moving rapidly — clearly a chemical change. Boiling water and dissolving sodium chloride are physical changes because no new substances are formed and the processes are reversible. Option D describes distillation, which is also a physical separation process, not a chemical change.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
The graph shows a curve that starts high and decreases over time, eventually levelling off — this shape is characteristic of a reactant being consumed as the reaction proceeds. Products such as ZnCl₂ and H₂ would show an increasing curve, while the concentration of HCl (a reactant) decreases as it is used up, matching the shape shown. The mass of Zn reacted would also increase over time, so it does not fit a decreasing curve. Therefore, the y-axis must represent the concentration of HCl, which starts at its initial value and falls to near zero as the acid is consumed.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Anhydrous copper(II) sulfate is a white powder that turns blue when water is added, as it absorbs water molecules to form hydrated copper(II) sulfate (CuSO₄·5H₂O) — this is a reversible reaction used as a chemical test for the presence of water. Anhydrous cobalt(II) chloride is blue and turns pink upon hydration, so it does not match the description. The hydrated forms of both compounds already contain water and would not undergo the same colour change upon addition of more water. Therefore, the substance that is white and turns blue with water is exclusively anhydrous copper(II) sulfate.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Reduction is defined as the loss of oxygen (or gain of electrons, or decrease in oxidation number). In option A, copper(II) oxide (CuO) loses its oxygen to carbon, forming copper metal (Cu) — the copper compound is reduced from Cu²⁺ to Cu⁰, losing oxygen in the process. Option B shows copper being oxidised (CuS gains oxygen to form CuO). Options C and D are purely physical state changes involving no chemical reaction at all, so no oxidation or reduction takes place. Therefore, only equation A represents the reduction of copper.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
To form magnesium sulfate with dilute sulfuric acid, the magnesium-containing solid must react with H₂SO₄ and supply Mg²⁺ ions. Magnesium metal (1) reacts with dilute H₂SO₄ to give MgSO₄ + H₂ ✓. Magnesium hydroxide (2) is a base that reacts with the acid in a neutralisation reaction to give MgSO₄ + H₂O ✓. Magnesium nitrate (3) is already a salt and does not react with dilute sulfuric acid to produce a different salt — it would simply dissolve or form an insoluble precipitate, not MgSO₄ ✗. Magnesium oxide (4) is a base that reacts with H₂SO₄ to give MgSO₄ + H₂O ✓. Therefore solids 1, 2 and 4 all produce magnesium sulfate.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Statement 1 is incorrect — ammonia is produced when ammonium salts react with a base (such as NaOH), not with an acid; adding ammonium nitrate to an acid would simply dissolve it. Statement 2 is correct — carbonates react with acids to produce CO₂ gas, causing visible effervescence (sodium carbonate + acid → salt + water + CO₂). Statement 3 is incorrect — methyl orange turns red/pink in acidic conditions, not yellow; yellow is the colour methyl orange shows in alkaline or neutral conditions. Statement 4 is correct — red litmus is already red and acids keep it red, as acids do not change red litmus. Therefore statements 2 and 4 are both correct.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
When excess solid copper(II) carbonate is added to dilute sulfuric acid, the reaction produces copper(II) sulfate solution, water and carbon dioxide gas. Because excess insoluble copper(II) carbonate is used (to ensure all the acid is consumed), filtration is needed to remove the unreacted solid from the copper(II) sulfate solution. The filtrate is then evaporated and allowed to cool slowly so that copper(II) sulfate crystals form — this is crystallisation. Distillation is not needed as we are not separating liquids, and titration is used only when both reactants are in solution (acid–alkali reactions), not when an excess insoluble solid is used.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
An element that forms X²⁻ ions gains 2 electrons to achieve a stable noble gas configuration, which means it has 6 outer-shell electrons in its neutral atom — placing it in Group VI of the Periodic Table. Elements in Group VI are non-metals (such as oxygen and sulfur), since the tendency to gain electrons and form negative ions is a characteristic of non-metallic elements on the right side of the Periodic Table. Metals lose electrons to form positive ions, so any option describing X as a metal or placing it in a group associated with positive ion formation is incorrect. Therefore, element X is a non-metal in Group VI.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Transition metals and their compounds are characteristically coloured due to the presence of partially filled d-orbitals in the transition metal ion. KMnO₄ (potassium manganate(VII)) contains manganese, which is a transition metal — this compound is well known for its intense purple/violet colour. The other three compounds — KNO₃, K₂CO₃ and K₂SO₄ — all contain potassium, which is a Group I alkali metal (not a transition metal), and their anions contain only non-transition elements; these compounds are all white solids with no colour. Therefore, only KMnO₄ is expected to be coloured.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Statement 1 is incorrect — reactivity decreases down Group VII, so chlorine is the most reactive of the three and iodine is the least reactive. Statement 2 is correct — chlorine (Cl₂), bromine (Br₂) and iodine (I₂) all exist as diatomic covalent molecules. Statement 3 is incorrect — at room temperature, chlorine is a gas, bromine is a liquid and iodine is a grey-black solid, so they are not all gases. Statement 4 is correct — all Group VII elements have 7 electrons in their outer shell, which is why they share similar chemical properties and all form X⁻ ions by gaining one electron.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Unreactive monatomic gases are the noble gases (Group VIII), which are characterised by having a completely full outer electron shell — this gives them no tendency to gain, lose or share electrons, making them chemically inert and existing as single atoms. From the electronic configurations shown, the elements with full outer shells are P (configuration 2, which is helium — full first shell) and S (configuration 2,8 or 2,8,8 — full outer shell, corresponding to neon or argon). Elements Q and R have incomplete outer shells and would therefore be reactive, forming compounds or molecules rather than existing as monatomic gases.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Non-metallic elements are generally characterised by poor electrical conductivity (they are insulators, with the exception of graphite), low melting points, brittleness (non-malleable), and low thermal conductivity. Metals, in contrast, are good conductors of electricity and heat, have high melting points, and are malleable and ductile. The correct row must show a combination of poor electrical conductivity and other non-metallic properties. Row B matches a non-metallic element by showing the absence of metallic properties such as good conductivity and malleability, consistent with typical non-metals like sulfur or phosphorus.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
In halogen displacement reactions, a more reactive halogen (X₂) displaces a less reactive halide ion (Y⁻) from solution, because reactivity decreases down Group VII. This means X must be higher (more reactive) than Y in the group, so X₂ displaces Y⁻ to form Y₂. Since halide ions in aqueous solution are colourless, the Y⁻ solution appears colourless. For example, if X₂ is chlorine (Cl₂) and Y⁻ is bromide (Br⁻), chlorine displaces bromine — the bromide ion solution is colourless, and this matches option B where X₂ is Cl₂ and Y⁻ (bromide) is colourless in aqueous solution.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
In this reaction, carbon reduces zinc oxide by removing its oxygen to form carbon monoxide (CO), while zinc metal is produced. Checking the atom balance for option C: Zn — 1 on each side ✓; O — 1 on each side ✓; C — 1 on each side ✓ — the equation is correctly balanced. Option A is unbalanced (1C cannot produce 1CO from 2ZnO without more oxygen accounted for). Options B and D suggest CO₂ as the product, which would require 2 oxygen atoms per carbon, but ZnO only supplies 1 oxygen per formula unit, making CO the correct carbon-containing product in this 1:1 ratio reaction.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Rusting of iron requires both oxygen and water to be present simultaneously. Even in an airtight container, if air (containing both oxygen and water vapour) is trapped inside, rusting can still occur over time. Replacing the air with argon — a noble gas — eliminates oxygen from the container entirely, removing one of the two essential conditions for rusting and therefore preventing it completely. Option A would introduce more oxygen and water. Option C would actually speed up rusting since higher temperatures increase reaction rates. Option D (sealing in a bag) does not remove the air already present and would not prevent rusting.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
In the blast furnace, the key reactions are: (i) C + O₂ → CO₂ (CO₂ is a product); (ii) C + CO₂ → 2CO (CO₂ is a reactant and CO is a product); (iii) Fe₂O₃ + 3CO → 2Fe + 3CO₂ (CO is a reactant and CO₂ is again a product). Therefore, carbon dioxide (2) is both produced in reactions (i) and (iii) and consumed as a reactant in reaction (ii). Carbon monoxide (3) is produced in reaction (ii) and consumed as a reactant in reaction (iii). Both substances act as reactants in some steps and products in others, making option C correct. Calcium carbonate decomposes but is only a reactant, and iron(III) oxide is only a reactant.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
The purity of water is determined by checking its physical properties against the known values for pure water. Pure water boils at exactly 100°C at standard pressure — any dissolved impurities will raise the boiling point above this value (boiling point elevation). Option A only tests for insoluble or non-volatile impurities and misses dissolved gases or volatile impurities. Option C tests for the presence of water (anhydrous cobalt(II) chloride turns from blue to pink) but does not confirm purity. Option D checks pH, which may be 7 for neutral impure water and would not detect non-ionic impurities. Therefore, checking the boiling point is the correct test for purity.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
An NPK fertiliser must supply all three essential plant nutrients: Nitrogen (N), Phosphorus (P) and Potassium (K). Checking option A — ammonium phosphate provides both nitrogen (from NH₄⁺) and phosphorus (from PO₄³⁻), while potassium sulfate provides potassium (from K⁺) — all three elements N, P and K are present ✓. Option B contains no potassium. Option C contains no phosphorus (calcium sulfate provides neither N, P nor K). Option D contains sodium instead of potassium, so K is absent. Only option A successfully provides all three required nutrients simultaneously.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Clean, dry air is composed of approximately 78% nitrogen and 21% oxygen, with only trace amounts of noble gases and carbon dioxide. Before air is liquefied for fractional distillation, it is first dried to remove water vapour and carbon dioxide is also removed (as it would solidify and block equipment), so neither water vapour nor carbon dioxide appear as products. Fractional distillation of liquid air then separates it based on different boiling points — nitrogen (b.p. −196°C) boils off first, followed by oxygen (b.p. −183°C) — making nitrogen and oxygen the two main products obtained.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Photosynthesis is the reaction in which carbon dioxide and water are converted to glucose and oxygen in the presence of chlorophyll, using light energy — the rate of this reaction directly increases with increasing light intensity, as light provides the energy required to drive the reaction. Option B is an acid-carbonate reaction that proceeds without light. Option C (addition of bromine to ethene) is a reaction that occurs in the dark as an electrophilic addition, not requiring light. Option D is combustion of methane, which is initiated by heat (ignition), not light. Therefore, only option A has its rate increased by light.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
To classify the three molecules correctly, each must be assessed for saturation and functional group. A saturated molecule contains only single carbon–carbon bonds (alkanes), while an unsaturated molecule contains at least one carbon–carbon double or triple bond (alkenes). The molecules shown include structures that can be identified by their C–C bond types and functional groups such as –OH (alcohol) or –COOH (carboxylic acid). The correct answer identifies which molecules are saturated or unsaturated and names their functional groups or homologous series accurately, matching the descriptions given in the answer table with the structural features visible in each displayed formula.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Petroleum is separated by fractional distillation into fractions based on the boiling points of the hydrocarbon chains they contain. Each fraction has a specific, well-established industrial use: the kerosene/paraffin fraction is used as jet fuel for aircraft, the diesel oil/gas oil fraction is used in diesel engines, the fuel oil fraction powers ships and home heating systems, and bitumen is used for surfacing roads. Options A, B, and C are incorrect because they each pair a fraction with the wrong use — for example, assigning bitumen to lubrication or gasoline to jet fuel would be incorrect. Option D correctly matches the named fraction with its standard industrial application as outlined in the syllabus.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Alkanes are hydrocarbons with the general formula CₙH₂ₙ₊₂, meaning they contain only carbon and hydrogen atoms (eliminating option C) joined exclusively by single covalent bonds (eliminating option D). Because all carbon–carbon bonds are single bonds, alkanes are classified as saturated compounds, making option A correct. They are also generally unreactive due to the strength and non-polarity of their C–C and C–H single bonds, only reacting under specific conditions such as combustion or photochemical substitution with chlorine, which rules out option B.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Clean, dry air is composed of approximately 78% nitrogen, 21% oxygen, and the remaining ~1% being noble gases and carbon dioxide. To find the volume of nitrogen in 200 cm³ of air, we calculate 78% of 200 cm³, which gives 78/100 × 200 = 156 cm³, approximately 160 cm³. Options A and B correspond roughly to 10% and 20% respectively, which are too low, while option C at 80 cm³ represents only 40% of the total volume. Option D at 160 cm³ is the closest approximation to the actual nitrogen content of 78%.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Rate of reaction is defined as the change in quantity of a reactant or product per unit time, so both a measurable quantity and a time measurement are required. The apparatus shown already includes a gas syringe to measure the volume of hydrogen gas produced, but to calculate rate (volume of gas ÷ time), a time-measuring instrument is also needed. A stop-watch provides this time measurement, allowing the student to record the volume of gas collected at regular time intervals and calculate the rate. A balance measures mass, a burette and volumetric pipette measure liquid volumes — none of these are needed when the gas syringe is already measuring the gas volume.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Ethanol has the molecular formula C₂H₅OH, belonging to the alcohol homologous series (CₙH₂ₙ₊₁OH). Its displayed formula must show all atoms and all bonds explicitly: two carbon atoms connected by a single C–C bond, five hydrogen atoms attached to the carbons (three on one carbon, two on the other), and a hydroxyl (–OH) functional group attached to the second carbon. The correct diagram therefore shows a chain of two carbons with the –OH group at one end and all individual C–H bonds drawn out. Any diagram showing a C=C double bond would represent an alkene, while a –COOH group would indicate a carboxylic acid, and a structure with only one carbon would be methanol.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Ethane has the molecular formula C₂H₆ (an alkane, CₙH₂ₙ₊₂ with n = 2), so options C and D are immediately eliminated as they show C₂H₄, which is the formula for ethene (an alkene), not ethane. Complete combustion requires sufficient oxygen to convert all carbon to carbon dioxide (CO₂) and all hydrogen to water (H₂O); incomplete combustion produces carbon monoxide (CO) instead, so option B is incorrect. Balancing option A: 2C₂H₆ gives 4C → 4CO₂ and 12H → 6H₂O, requiring 4×2 + 6 = 14 oxygen atoms = 7O₂, confirming the equation is correctly balanced.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
The state symbol (s) next to Ca(OH)₂ in the equation shows that calcium hydroxide is produced as an insoluble solid precipitate, while sodium nitrate remains dissolved in the aqueous solution. To separate an insoluble solid from a liquid mixture, filtration is the appropriate technique — the solid is retained in the filter paper while the liquid filtrate passes through. Chromatography separates dissolved substances, crystallisation is used to obtain a dissolved solute from solution, and distillation separates liquids based on different boiling points — none of these are suitable for removing an insoluble solid precipitate.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
The two tests identify both the cation and the anion present in compound X. Adding aqueous sodium hydroxide to the solution produces a red-brown precipitate that is insoluble in excess, which is the characteristic result for iron(III) ions (Fe³⁺); iron(II) ions would instead give a green precipitate, ruling out options B and D. The second test for the anion shows no white precipitate with acidified barium nitrate solution, confirming the absence of sulfate ions (SO₄²⁻) and eliminating options C and D; the anion is therefore nitrate (NO₃⁻). Combining Fe³⁺ with NO₃⁻ gives iron(III) nitrate, Fe(NO₃)₃.
✅ Answer: (A)
✅ Answer: (A)