▶️ Answer/Explanation
In a solid such as ice, particles are held in fixed positions in a regular lattice by strong forces of attraction, but they are not completely stationary — they continuously vibrate about their fixed positions. This makes option D correct. Option A is wrong because molecules in steam (a gas) are the furthest apart, not the closest. Option B is incorrect because molecules in water (a liquid) have intermediate separation — it is the gas state (steam) where molecules are furthest apart. Option C is wrong because steam, being the highest energy state, has the highest average molecular velocity, not the second highest.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
A substance exists as a liquid when the temperature is above its melting point but below its boiling point. At −200 °C: Argon has a melting point of −189 °C and a boiling point of −186 °C — since −200 °C is below argon’s melting point, argon is a solid. Nitrogen has a melting point of −210 °C and a boiling point of −196 °C — since −200 °C is above nitrogen’s melting point and below its boiling point, nitrogen is a liquid. Oxygen has a melting point of −219 °C and a boiling point of −183 °C — since −200 °C is above oxygen’s melting point and below its boiling point, oxygen is a liquid. Therefore, exactly two samples (nitrogen and oxygen) are liquids at −200 °C.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
A compound is a pure substance formed when two or more elements are chemically combined in fixed proportions, and the resulting substance has properties entirely different from those of its constituent elements; it can only be separated by chemical means. Option B describes a mixture, where elements or compounds are physically combined and retain their individual properties. Option C refers to an alloy, which is actually a mixture (not a compound) of a metal with other elements. Option D also describes a mixture, since mixtures can be separated by physical methods such as filtration, distillation or chromatography.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Potassium (atomic number 19) has the electronic configuration 2,8,8,1; when it forms K⁺ it loses one electron, giving 2,8,8. Chlorine (atomic number 17) has the configuration 2,8,7; when it forms Cl⁻ it gains one electron, giving 2,8,8. Both ions therefore have the identical electronic configuration 2,8,8, making option A correct. Option B is wrong because Ca²⁺ loses its two outer electrons from the configuration 2,8,8,2, leaving 2,8,8 — not 2,8,8,2. Option C is incorrect because halogens are in Group VII (not VI) and have seven outer shell electrons. Option D is wrong because although magnesium is in Period 3 (configuration 2,8,2), the Mg²⁺ ion loses its two outer electrons, leaving only two occupied shells (2,8).
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Bromine is a halogen in Group VII with seven outer shell electrons; it gains one electron to achieve a stable noble gas configuration, forming the negatively charged bromide ion (Br⁻), making option A correct. Option B is incorrect because ionic bonds form between a metal (typically from Groups I or II) and a non-metal (typically from Group VII), not between two Group VII elements. Option C is wrong because positive ions (cations) are formed when atoms lose electrons, not protons — the number of protons in the nucleus never changes during ion formation. Option D is incorrect because in potassium iodide (KI), potassium forms a positively charged K⁺ ion, while iodide (I⁻) carries the negative charge.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Each covalent bond consists of one shared pair of electrons, so counting shared pairs is the same as counting the number of covalent bonds in the molecule. CH₄ has four C–H bonds, giving four shared pairs. Cl₂ has one Cl–Cl bond, giving only one shared pair. HCl has one H–Cl bond, giving only one shared pair. H₂O has two O–H bonds, giving exactly two shared pairs of electrons, making option D the correct answer. The two lone pairs on the oxygen atom in H₂O are not shared and must not be confused with the bonding pairs.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
In graphite, each carbon atom forms three covalent bonds with neighbouring carbon atoms in flat hexagonal layers, leaving one electron per atom that is not used in bonding. These delocalised (mobile) electrons are free to move throughout the layers, allowing graphite to conduct electricity — which is precisely the property required for use as an electrode. Option A is incorrect because graphite contains no ions; it is a covalently bonded structure. Option B, while true, does not by itself explain electrical conductivity, since diamond also has a giant covalent structure yet cannot conduct electricity because it has no mobile electrons. Option C is incorrect because graphite is a non-metal.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
To balance the equation, count atoms on each side. One CH₄ molecule contains 1 carbon and 4 hydrogen atoms. Combustion produces 1 CO₂ (accounting for the 1 carbon) and 2 H₂O (accounting for all 4 hydrogen atoms). The total oxygen required on the right-hand side is 2 (from CO₂) + 2 (from 2H₂O) = 4 oxygen atoms, which requires 2 O₂ molecules on the left. This gives the balanced equation: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g), confirming option B. Options A and D have incorrect numbers of O₂ molecules, and option C has only one H₂O, leaving hydrogen atoms unbalanced.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
The question involves simple proportional reasoning: 7.29 g of magnesium is exactly three times 2.43 g (since 7.29 ÷ 2.43 = 3). Since the reaction is carried out with excess steam, magnesium is the limiting reactant, and the amounts of products formed are directly proportional to the amount of magnesium used. Multiplying both products by 3: magnesium oxide = 4.03 × 3 = 12.09 g, and hydrogen = 0.20 × 3 = 0.60 g. Options A and B use incorrect multipliers, and option C uses a factor of 2 instead of 3.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
During electrolysis, the cathode is the negative electrode, connected to the negative terminal of the power supply. Positively charged hydrogen ions (H⁺) are attracted to the negatively charged cathode, where they gain electrons and are discharged to form hydrogen gas: 2H⁺ + 2e⁻ → H₂. In the diagram, electrode B is connected to the negative terminal of the battery, making it the cathode — and therefore the electrode at which hydrogen is produced. The anode (positive electrode) is where non-metal ions such as Cl⁻ or OH⁻ are discharged instead.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
A hydrogen–oxygen fuel cell generates electricity through an electrochemical reaction between hydrogen and oxygen, with water as the only chemical product — making it a clean and environmentally friendly energy source. Hydrogen is supplied at the anode where it is oxidised, releasing electrons that flow through the external circuit to generate electricity, while oxygen is supplied at the cathode where it is reduced. Options A, B and D are all incorrect because carbon dioxide and methane are not reactants in a fuel cell; in fact, the absence of carbon-containing reactants is what makes hydrogen fuel cells attractive since no carbon dioxide is produced during operation.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
In a reaction pathway diagram, if the products are at a higher energy level than the reactants, the reaction is endothermic — the system absorbs energy from the surroundings, making ΔH positive. The diagram shown has products at a higher energy than the reactants, confirming statement 1 is correct and statement 2 is wrong. The thermal decomposition of limestone (CaCO₃ → CaO + CO₂) is a well-known endothermic reaction that requires continuous heating to proceed, which matches the diagram. The combustion of methane is strongly exothermic (products at lower energy than reactants), so statement 3 is incorrect. Therefore, statements 1 and 4 are both correct.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
A chemical change produces one or more new substances with different chemical properties from the original, is generally irreversible, and is usually accompanied by an energy change (heat, light, etc.). A physical change, by contrast, does not produce any new substance — the original material can be recovered by simple physical means. Row B describes a chemical change: a new substance is formed, the process is not easily reversible, and a temperature change (energy transfer) accompanies the reaction. The other rows describe physical changes such as changes of state or dissolving, where no new substance is formed and the original material can be recovered.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Statement 2 is correct: increasing temperature gives particles more kinetic energy, leading to more frequent and more energetic collisions, so the magnesium disappears faster. Statement 4 is also correct: the rate of reaction can be measured by the rate at which a reactant is consumed, so the faster the magnesium disappears, the faster the rate of reaction. Statement 1 is wrong because smaller particles provide a greater total surface area, which increases the frequency of collisions and speeds up hydrogen production — not slows it down. Statement 3 is incorrect because a lower concentration of hydrochloric acid means fewer H⁺ ions per unit volume, resulting in fewer collisions per second and a slower rate of reaction, not a faster one.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Cobalt(II) chloride exists in two forms that are interconverted in a reversible reaction: the hydrated form (CoCl₂·6H₂O) is pink, and the anhydrous form (CoCl₂) is blue. When hydrated cobalt(II) chloride is heated, the water of crystallisation is driven off, converting the pink hydrated form into the blue anhydrous form — making option A correct. Option B is wrong because adding water to the anhydrous (blue) form, not the hydrated form, produces the blue-to-pink colour change. Option C is incorrect because adding water to anhydrous cobalt(II) chloride turns it pink, not the hydrated form. Option D is wrong because heating produces the blue anhydrous form, not a white substance.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
The only alkaline gas produced in common chemistry reactions is ammonia (NH₃). Ammonia is released when a base reacts with an ammonium salt — specifically, when a hot alkali or base reacts with an ammonium compound. The reaction that fits all the criteria (producing an alkaline gas, a salt, and water) is that of a base reacting with an ammonium salt: for example, sodium hydroxide (aqueous solution) reacting with ammonium chloride (solid) produces ammonia gas, sodium chloride (a salt), and water. This matches option D, where the aqueous solution is an alkali (such as NaOH) and the solid is an ammonium salt (such as NH₄Cl).
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Calcium oxide (CaO) is a metal oxide and is classified as a basic oxide — it reacts with acids to form a salt and water but does not dissolve readily in water. Calcium hydroxide (Ca(OH)₂) is a base that partially dissolves in water to form an alkaline solution, so it is classified as an alkali. Sulfur dioxide (SO₂) is an oxide of the non-metal sulfur; it dissolves in water to form sulfurous acid and is therefore classified as an acidic oxide. This combination — basic oxide, alkali, and acidic oxide — matches option D, and it also explains why CaO and Ca(OH)₂ are effective at neutralising the acidic SO₂ in flue gases.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
When preparing a pure soluble salt such as copper(II) sulfate from an acid and an insoluble carbonate, it is essential that all of the acid is consumed; any remaining sulfuric acid in the final solution would contaminate the copper(II) sulfate product. By adding excess copper(II) carbonate, all the sulfuric acid is guaranteed to react completely, leaving only the insoluble excess carbonate behind, which can then be easily removed by filtration. Option A is incorrect because adding excess copper(II) carbonate means some of it will remain unreacted. Option C is wrong because excess solid does not significantly increase the rate once the acid is the limiting factor. Option D is incorrect because the amount of product is determined by the amount of acid present, not by adding more carbonate beyond what is needed.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
In the Periodic Table, the group number tells us the number of electrons in the outer shell, and the period number tells us the number of occupied electron shells. An element with two electrons in its outer shell belongs to Group II, and an element with three occupied electron shells is in Period 3. The element that satisfies both conditions — Group II and Period 3 — is magnesium (Mg), which has the electronic configuration 2,8,2: two inner shells fully filled and a third outer shell containing exactly two electrons. This corresponds to option C in the diagram.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
The three properties given are all characteristic of Group I alkali metals: they have low melting points (lithium 181 °C, sodium 98 °C, potassium 63 °C — a melting point of 64 °C is consistent with potassium), very low densities well below 1 g/cm³ for lighter members and just above for heavier ones (0.86 g/cm³ matches potassium), and they react vigorously with water to produce hydrogen gas and a metal hydroxide solution. Group 0 noble gases are unreactive and do not react with water. Group VII halogens are non-metals with very different physical properties. Transition metals have high melting points, high densities, and do not react vigorously with cold water. All evidence points to element X being a Group I alkali metal.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Titanium is a transition metal, located in the d-block of the Periodic Table between Groups II and III. All transition metals share a set of characteristic properties that distinguish them from Group I and Group II metals: they have high melting points, high densities, form coloured compounds, and can act as catalysts. Additionally, transition metals exhibit variable oxidation states — for example, titanium commonly forms Ti²⁺, Ti³⁺ and Ti⁴⁺ ions. The correct row (B) reflects these properties: high melting point, high density, coloured compounds, and variable oxidation states. Rows describing low melting points, low densities, or fixed oxidation states would be characteristic of Group I or Group II metals instead.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
Brass is an alloy, and an alloy is defined as a mixture of a metal with one or more other elements — the components are physically combined, not chemically bonded, so brass is a mixture rather than a compound. Brass is specifically a mixture of copper and zinc, typically containing about 60–70% copper and 30–40% zinc, and is harder and stronger than either pure copper or pure zinc alone. Options A and B are incorrect because brass is a mixture, not a compound — the elements retain their individual identities and no new substance with fixed composition is formed. Option D is incorrect because the second metal in brass is zinc, not tin (tin is used in bronze, a different alloy).
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Aluminium (symbol Al) has a very low density of approximately 2.7 g/cm³, which is about one-third the density of steel (iron), making it ideal for aircraft construction where minimising weight is critical for fuel efficiency and performance. In addition to its low density, aluminium also offers good strength (especially when alloyed), excellent resistance to corrosion due to its protective oxide layer, and good workability. Copper (Cu) is used in electrical wiring due to its conductivity, iron (Fe) is used in construction but is too dense and prone to rusting for aircraft, and zinc (Zn) is primarily used in galvanising to protect iron from corrosion — none of these are selected for aircraft manufacture on the basis of low density.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
Stainless steel is an alloy of iron with chromium, nickel and carbon; the chromium content (typically around 10–18%) forms a thin, stable oxide layer on the surface that protects the alloy from corrosion and rusting, making it highly resistant to moisture and food acids encountered during everyday use of cutlery. This resistance to rusting is the key property that makes stainless steel ideal for knives, forks and spoons, which come into regular contact with water and food. Option A is irrelevant to cutlery use. Option B, a high melting point, is a general property of metals but is not the specific reason stainless steel is chosen for cutlery. Option D, ductility, relates to the ability to be drawn into wires, which is not a requirement for cutlery manufacture.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Using the reactivity series to evaluate each reaction: (1) Calcium is above hydrogen in the reactivity series and reacts vigorously with cold water to produce calcium hydroxide and hydrogen gas — correct. (2) Silver is below hydrogen in the reactivity series and therefore does not react with dilute hydrochloric acid to produce hydrogen — incorrect. (3) Magnesium is above hydrogen in the reactivity series and reacts with steam to produce magnesium oxide and hydrogen gas — correct. (4) Zinc is above hydrogen in the reactivity series and reacts with dilute hydrochloric acid to produce zinc chloride and hydrogen gas — correct. Therefore reactions 1, 3 and 4 all produce hydrogen gas, making option A correct.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
The reactivity of a metal can be determined by comparing how vigorously it reacts with water, steam and dilute acid — more reactive metals react with less energetic reagents. Lithium reacts with cold water, placing it highest in reactivity among the three. Manganese does not react with cold water but does react with steam, placing it in an intermediate position. Tin does not react with steam but does react with dilute hydrochloric acid, placing it as the least reactive of the three. Therefore the correct order from most to least reactive is: lithium > manganese > tin, which corresponds to option D.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
Rusting is the corrosion of iron to form hydrated iron(III) oxide (Fe₂O₃·xH₂O), and both water and oxygen must be present simultaneously for this process to occur — neither alone is sufficient. This is confirmed by classic experiments where iron nails kept in dry air (oxygen but no water) or in boiled, sealed water (water but no dissolved oxygen) do not rust, whereas nails exposed to both water and oxygen rust readily. Salt (such as sodium chloride) can accelerate the rate of rusting by acting as an electrolyte, but it is not a required condition for rusting to begin. Therefore option C correctly identifies the two essential substances needed for iron to rust.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
In the blast furnace, coke (carbon) is burned in the hot air blast to produce carbon dioxide: C + O₂ → CO₂. This is a combustion reaction, which is a type of oxidation reaction — the carbon is oxidised by gaining oxygen. Limestone (calcium carbonate, CaCO₃) is heated and undergoes thermal decomposition: CaCO₃ → CaO + CO₂, breaking down into calcium oxide and carbon dioxide. Thermal decomposition is not a redox reaction; it simply involves a compound splitting into simpler substances upon heating. Therefore, coke undergoes combustion (oxidation) and limestone undergoes thermal decomposition, which corresponds to option B.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
At a waterworks, water undergoes three main treatment stages: sedimentation and filtration remove insoluble solid particles; activated carbon removes unpleasant tastes and odours; and chlorination kills harmful microbes and bacteria. After these treatments, insoluble substances and bacteria are removed or destroyed, but soluble substances — including naturally dissolved mineral salts and chlorine compounds introduced during chlorination — remain dissolved in the water and cannot be removed by these processes. Option A is wrong because both bacteria and insoluble substances are removed during treatment. Option B is incorrect because chlorination specifically kills bacteria. Option D is wrong because other soluble mineral substances also remain, not just chlorine compounds.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
NPK fertilisers must supply three essential elements for improved plant growth: nitrogen (N), phosphorus (P) and potassium (K). From the image, the four compounds are typically: W = KCl (contains K only), X = (NH₄)₃PO₄ or a compound containing both N and P, Y = KNO₃ (contains K and N), and Z = a compound containing only one of the elements. Compound X contains both nitrogen and phosphorus, while compound Y contains both potassium and nitrogen — together X and Y provide all three elements N, P and K. No other pair of compounds from the options supplies all three elements simultaneously. This makes option C (X and Y) the correct combination for an NPK fertiliser.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
Clean, dry air contains approximately 78% nitrogen, 21% oxygen, small amounts of noble gases, and about 0.04% carbon dioxide — CO₂ is therefore already present in clean air. Reaction 1 produces carbon monoxide (CO) from the incomplete combustion of methane; CO is toxic and is not present in clean air, making it a pollutant. Reaction 2 produces only water, which is present in air. Reaction 3 produces CO₂, which is already a natural component of clean air, so it is not a gas “not present in clean air.” Reaction 4 produces nitrogen monoxide (NO), an oxide of nitrogen that is not present in clean air and is a harmful pollutant causing acid rain and respiratory problems. Therefore reactions 1 and 4 produce gases not found in clean air.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
The molecular structure shown contains a carbon chain with a hydroxyl (–OH) functional group attached, which is the defining feature of the alcohol homologous series with the general formula CnH2n+1OH. The molecule also contains only single carbon–carbon bonds, confirming it is saturated and belongs to the alcohols rather than alkenes or carboxylic acids. Carboxylic acids would require a –COOH group, alkenes would have a C=C double bond, and alkanes would have no functional group other than C–H bonds. Since the –OH group is clearly present on the structure without a carbonyl (C=O) group adjacent to it, the correct classification is the alcohol homologous series.
✅ Answer: C
✅ Answer: C
▶️ Answer/Explanation
According to the Cambridge IGCSE syllabus, each petroleum fraction has a specific, well-defined use: the kerosene/paraffin fraction is used as jet fuel, and the bitumen fraction is used for making roads — these correspond to rows 3 and 4 respectively. Row 1 is incorrect because the refinery gas fraction is used for heating and cooking, not as a fuel for cars (that is the gasoline/petrol fraction). Row 2 is incorrect because the naphtha fraction serves as a chemical feedstock, not as a lubricant (lubricating oils come from a heavier fraction). Since only rows 3 and 4 correctly match each fraction to its proper use, the answer is D.
✅ Answer: D
✅ Answer: D
▶️ Answer/Explanation
Ethanol is manufactured by fermentation, in which glucose is broken down by yeast enzymes to produce ethanol and carbon dioxide; yeast acts as a biological catalyst and is not consumed as a reactant, so it does not appear as a reactant in the word equation itself. Option B is incorrect because water is not a product of fermentation — it incorrectly lists yeast as a reactant and water as a product. Option C is wrong because ethane (an alkane) does not react with water to form ethanol under normal conditions. Option D is incorrect because the addition of steam to ethene produces only ethanol with no carbon dioxide as a by-product. Therefore, the correct word equation for fermentation is simply glucose → ethanol + carbon dioxide.
✅ Answer: A
✅ Answer: A
▶️ Answer/Explanation
Ethanoic acid (CH3COOH) is a weak acid, meaning it only partially dissociates in aqueous solution, producing a relatively low concentration of H+ ions — this gives it a pH greater than 1 but still below 7, making it acidic. Being an acid, it turns blue litmus red and reacts with carbonates to produce carbon dioxide, with metals to produce hydrogen gas, and with bases to form a salt and water. Any row suggesting it is a strong acid (fully dissociated), has a neutral or alkaline pH, or turns litmus blue would be incorrect. The correct row B identifies ethanoic acid as a weak acid with the expected acidic behaviour toward indicators and its characteristic reactions.
✅ Answer: B
✅ Answer: B
▶️ Answer/Explanation
By definition, a polymer is a large molecule formed by the joining together of many small repeating units called monomers; this means monomers are small molecules while polymers are large molecules. During polymerisation, hundreds or thousands of monomer units link together through covalent bonds to form one very long polymer chain, so the polymer molecule is significantly larger than the individual monomer. Any row suggesting monomers are large or that both are the same size would contradict the fundamental definition of polymerisation. Therefore, the correct row C correctly identifies monomers as small and polymers as large.
✅ Answer: C
✅ Answer: C
▶️ Answer/Explanation
To measure a mass of 2.00 g of powdered calcium carbonate accurately to two decimal places, a balance (weighing scale) must be used, as it is the only instrument capable of measuring mass with that level of precision. To measure a volume of 50.0 cm3 of hydrochloric acid, a measuring cylinder is the appropriate choice — a burette would be unnecessarily precise for this volume and is typically reserved for titrations, while a volumetric pipette is designed only for fixed standard volumes. A balance paired with a measuring cylinder therefore gives the correct combination of instruments for this experiment, making option A the correct answer.
✅ Answer: A
✅ Answer: A
▶️ Answer/Explanation
In a chromatogram, each distinct spot at a different Rf value represents a chemically different dye; spots appearing at the same height across different lanes indicate the same dye is present in both samples. To find the number of different red dyes across all three sweets X, Y and Z, you must count only the spots identified as red that have distinct Rf values — spots at the same level in different lanes count as only one dye. Examining the chromatogram, there are two red spots at different Rf values across the three sweets, meaning two chemically distinct red dyes are present in total. Counting shared spots only once and distinguishing them by their travel distance from the baseline gives a total of 2 different red dyes.
✅ Answer: B
✅ Answer: B
▶️ Answer/Explanation
The mixture contains two components that must be separated in a logical sequence: sand is an insoluble solid suspended in the sodium chloride solution, so filtration must be performed first — this retains the sand as a residue on the filter paper while the sodium chloride solution passes through as the filtrate. Once the sand has been removed, the sodium chloride solution (filtrate) can then be subjected to crystallisation, where the water is carefully evaporated to allow solid sodium chloride crystals to form. Options A and B reverse or incorrectly apply the steps, and option D introduces distillation which would only recover water, not solid sodium chloride. Therefore, filtration followed by crystallisation is the correct two-step process.
✅ Answer: C
✅ Answer: C
▶️ Answer/Explanation
The two observations together uniquely identify compound M: a lilac flame in a flame test is the characteristic result for potassium ions (K+), which immediately eliminates options A and B as both contain sodium (which gives a yellow flame). The second test — a gas that turns limewater cloudy when dilute hydrochloric acid is added — confirms the presence of carbonate ions (CO32–), since carbonates react with acids to produce carbon dioxide, which is the gas that turns limewater milky; this eliminates option C (potassium sulfate) as sulfates do not produce carbon dioxide with acid. Combining both results, the compound must contain both potassium ions and carbonate ions, making it potassium carbonate.
✅ Answer: D
✅ Answer: D