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Q1. Corrosion causes damage to:
All of theseCorrosion affects all iron and steel structures exposed to moisture, oxygen, and environmental pollutants. Car bodies develop rust patches that eat through metal, railings weaken and become unsafe, and bridges suffer structural degradation that requires expensive maintenance. The economic cost of corrosion runs into billions of dollars annually worldwide.
Q2. Reaction Fe₂O₃ + Al → Al₂O₃ + Fe is:
DisplacementThis is the thermite reaction: Fe₂O₃ + 2Al → Al₂O₃ + 2Fe. Aluminium (more reactive) displaces iron (less reactive) from iron(III) oxide. It is a single displacement reaction, not double displacement, because one element (Al) replaces another element (Fe) in a compound. The reaction is highly exothermic (produces molten iron) and is used for welding railway tracks.
Q3. NaOH + H₂SO₄ forms:
Na₂SO₄ + H₂OThis is a neutralization reaction between a base (sodium hydroxide) and an acid (sulphuric acid). The balanced equation is: 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O. Sodium sulphate (salt) and water are the products. This reaction is exothermic (releases heat).
Q4. In PbO + C → Pb + CO₂, carbon is:
OxidisedIn this reaction, carbon (C) gains oxygen to form carbon dioxide (CO₂). Gaining oxygen is oxidation. Meanwhile, lead in PbO loses oxygen to become elemental lead (Pb) — that is reduction. So carbon is the substance that gets oxidized. This reaction is used in the extraction of lead from its ore.
Q5. Which metal tarnishes black?
SilverSilver tarnishes black due to the formation of silver sulphide (Ag₂S). Silver reacts with hydrogen sulphide (H₂S) present in air from industrial pollution, volcanic emissions, or decaying organic matter. The reaction is: 2Ag + H₂S + ½O₂ → Ag₂S (black) + H₂O. Zinc and iron rust (reddish-brown), copper turns green (patina).
Q6. Potassium reacts with water to give:
KOH + H₂Potassium is an extremely reactive alkali metal. The reaction with water is: 2K + 2H₂O → 2KOH + H₂ (hydrogen gas). This reaction is so vigorous that the heat released ignites the hydrogen gas, producing a lilac flame (characteristic of potassium). The solution becomes strongly alkaline due to potassium hydroxide formation.
Q7. Green coating forms on:
CopperWhen copper is exposed to moist air containing oxygen, carbon dioxide, and water, it forms a green coating of basic copper carbonate, Cu₂(OH)₂CO₃. This is commonly seen on old copper roofs (like the Statue of Liberty), copper statues, and old copper coins. Lead forms a dull grey coating, iron rusts reddish-brown, zinc forms a white/grey coating.
Q8. Reaction where both oxidation and reduction occur is called:
Redox reaction“Redox” is a contraction of reduction-oxidation. In any chemical reaction where one species loses electrons (oxidation), another species must gain those electrons (reduction). They occur simultaneously — you cannot have one without the other. Examples include displacement reactions, combustion, rusting, and many decomposition reactions.
Q9. Chips packets are filled with:
NitrogenChips packets are flushed with nitrogen gas before sealing. Nitrogen is inert (non-reactive) and does not react with the food. By displacing oxygen, it creates an oxygen-free environment, preventing oxidation of fats and oils in the chips. This prevents rancidity and keeps chips fresh for longer periods.
Q10. Silver tarnish is example of:
CorrosionTarnishing of silver is a type of corrosion. Corrosion is the gradual destruction of metals by chemical reactions with the environment. In silver’s case, it reacts with hydrogen sulphide (H₂S) in air to form black silver sulphide (Ag₂S). Unlike iron rusting which causes flaking and structural damage, silver tarnish is a surface layer that can be polished off.
Q11. Which statement is incorrect?
A. CO₂ oxidizedIn the reaction PbO + C → Pb + CO₂, carbon (C) is oxidized to CO₂ (gains oxygen). Lead in PbO is reduced to Pb (loses oxygen). CO₂ is the product — it cannot be further oxidized under these conditions. So saying “CO₂ oxidized” is incorrect. Pb is the product that has been reduced, PbO is the compound that got reduced, and carbon was oxidized.
Q12. Hydrogen + nitrogen forms:
NH₃N₂ + 3H₂ ⇌ 2NH₃ (ammonia). This is the Haber process, one of the most important industrial chemical reactions. The reaction is reversible and requires high pressure (200 atmospheres), high temperature (450°C), and an iron catalyst. Ammonia is used primarily to produce fertilizers (urea, ammonium nitrate) and also for explosives and cleaning products.
Q13. Antioxidants stop:
OxidationAntioxidants prevent or slow down oxidation reactions. They work by being oxidized themselves instead of the substance they are protecting. Common food antioxidants include vitamin C (ascorbic acid), vitamin E (tocopherols), BHA, and BHT. They are added to fatty foods, oils, and processed foods to prevent rancidity and extend shelf life.
Q14. Burning of H₂S forms:
H₂O + SO₂Hydrogen sulphide (rotten egg smell) burns in the presence of sufficient oxygen according to: 2H₂S + 3O₂ → 2SO₂ + 2H₂O. The products are sulphur dioxide (a pungent, irritating gas) and water vapour. This reaction is used in the Claus process to recover sulphur from H₂S in natural gas and petroleum refining.
Q15. Airtight containers prevent:
OxidationAirtight containers prevent oxygen from reaching the food. Since oxidation of fats and oils requires oxygen to proceed, removing oxygen effectively stops or greatly slows the reaction. This is why potato chip bags are sealed airtight — to prevent the chips from becoming rancid. While airtight containers also prevent evaporation, the primary chemical concern is preventing oxidation.
Q16. Reduction involves:
Loss of oxygenIn the classical definition, reduction is the loss of oxygen from a substance. For example, in the reaction CuO + H₂ → Cu + H₂O, copper oxide loses oxygen to become copper metal. This definition is especially useful in metallurgy, where metal ores (oxides) are reduced to obtain pure metals. The modern definition is gain of electrons.
Q17. In the same reaction, PbO is:
ReducedIn the reaction PbO + C → Pb + CO₂, lead oxide (PbO) loses oxygen to become elemental lead (Pb). Loss of oxygen is reduction. Therefore, PbO is reduced. At the same time, carbon gains oxygen (is oxidized). This is a classic redox reaction where the metal oxide is reduced to metal.
Q18. Reaction of HCl with iron gives:
Hydrogen + iron chlorideFe + 2HCl → FeCl₂ (iron(II) chloride) + H₂ (hydrogen gas). This is a single displacement reaction where iron (more reactive than hydrogen) displaces hydrogen from hydrochloric acid. The hydrogen gas is released as effervescence (bubbles). This reaction is commonly used in laboratories to produce small amounts of hydrogen gas.
Q19. Rusting of iron is a:
Chemical changeRusting is a chemical change because iron (Fe) reacts with oxygen (O₂) and water (H₂O) to form a new substance — hydrated iron(III) oxide (Fe₂O₃·xH₂O) — which has different chemical properties. The change is permanent (cannot be reversed easily), new substances are formed, and there is a change in color from grey metallic to reddish-brown.
Q20. In redox reaction:
One is oxidised and other reducedThe defining characteristic of a redox reaction is that oxidation and reduction occur simultaneously. One species loses electrons (is oxidized) and another species gains those electrons (is reduced). They are complementary processes — you cannot have oxidation without reduction, or reduction without oxidation.
Q21. Burning of magnesium ribbon shows magnesium is:
OxidisedWhen magnesium burns: 2Mg + O₂ → 2MgO. Magnesium gains oxygen to form magnesium oxide. According to the definition, gaining oxygen is oxidation. So magnesium is oxidized. This reaction produces intense white light and a lot of heat, making it exothermic. The white powder formed is magnesium oxide.
Q22. In CuSO₄ and Fe reaction, copper is:
ReducedFe + CuSO₄ → FeSO₄ + Cu. Copper ions (Cu²⁺) gain 2 electrons to become copper metal (Cu). Gain of electrons is reduction. Iron loses electrons (oxidation) simultaneously. The copper is reduced from a +2 oxidation state to 0. This is why we see reddish-brown copper depositing on the iron nail.
Q23. Nitrogen is used because it:
Prevents oxidationNitrogen is an inert gas — it does not react with food at room temperature. When flushed into food packets, it displaces oxygen, creating an oxygen-free environment. Since oxidation of fats and oils requires oxygen, preventing oxygen contact prevents rancidity. This extends the shelf life of packaged foods like chips, nuts, and coffee.
Q24. AgNO₃ + NaCl produces:
NaNO₃ + AgClAgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq). This is a double displacement/precipitation reaction. Silver chloride (AgCl) is insoluble in water and forms a curdy white precipitate. Sodium nitrate remains dissolved. This reaction is used as a test for chloride ions — the formation of a white precipitate that darkens in sunlight confirms the presence of Cl⁻ ions.
Q25. Magnesium burns to form:
Magnesium oxide2Mg + O₂ → 2MgO. Magnesium reacts with oxygen (from air) to form magnesium oxide. The reaction produces a dazzling white light and a lot of heat, so it is used in flashbulbs, fireworks, and flares. The product is a white powder that turns red litmus blue (basic oxide) and reacts with water to form magnesium hydroxide.
Q26. Black coating forms on:
SilverSilver develops a black coating of silver sulphide (Ag₂S) due to reaction with hydrogen sulphide (H₂S) present in air. This is tarnishing. Aluminium forms a protective transparent oxide layer (not black). Iron rusts reddish-brown. Zinc forms a white/grey coating of zinc carbonate or zinc oxide.
Q27. Rancidity occurs in:
Cooking oilRancidity specifically refers to the oxidation of fats and oils. Cooking oils contain unsaturated fatty acids that react with atmospheric oxygen, producing volatile aldehydes, ketones, and carboxylic acids that give a bad smell and taste. Iron rusts (corrosion), water and salt do not undergo rancidity.
Q28. A substance is reduced if it:
Loses oxygenThe classical definition states that reduction is the loss of oxygen from a substance. For example, when copper oxide is heated with hydrogen: CuO + H₂ → Cu + H₂O, copper oxide loses oxygen and is reduced to copper metal. The modern definition is gain of electrons, but the loss of oxygen definition is still widely used.
Q29. Substances that prevent oxidation are:
AntioxidantsAntioxidants are compounds that prevent or slow down oxidation reactions. They work by being oxidized themselves instead of the substance they protect. Common natural antioxidants include vitamin C (ascorbic acid), vitamin E (tocopherols), flavonoids, and carotenoids. Synthetic antioxidants include BHA, BHT, and TBHQ, added to processed foods.
Q30. Rusting of iron is called:
CorrosionRusting is the specific term for corrosion of iron and its alloys. Corrosion is the broader term for the deterioration of any metal due to chemical reactions with its environment. While rusting involves oxidation (iron reacting with oxygen), the correct classification is corrosion. Rust is hydrated iron(III) oxide, Fe₂O₃·xH₂O.
Q31. Food becomes bad smelling due to:
OxidationWhen fats and oils in food undergo oxidation (rancidity), they produce volatile organic compounds such as aldehydes, ketones, and short-chain fatty acids. These compounds have sharp, unpleasant odours described as “off” or “rancid.” This is why old cooking oil, stale chips, and expired nuts develop a bad smell.
Q32. Green coating on copper is example of:
CorrosionThe green coating (basic copper carbonate) on copper is a form of corrosion. While it involves oxidation, corrosion is the correct broader term. This patina actually protects the underlying copper from further corrosion, unlike iron rust which flakes off and exposes fresh metal. This is why copper roofs and statues last for centuries.
Q33. Nitrogen gas is used in food packing because it is:
InertNitrogen is chemically inert at room temperature — it does not react with food components. This makes it ideal for displacing oxygen without affecting the food. While it is neither toxic nor unusually heavy, its inertness is the key property. Argon (another inert gas) is sometimes used for more sensitive products.
Q34. In oxidation-reduction reactions:
Both occur togetherOxidation and reduction are simultaneous and complementary processes. When one substance loses electrons (oxidation), another substance must gain those electrons (reduction). They cannot occur independently. This is captured in the mnemonic OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).
Q35. Oxidation can also be defined as:
Gain of oxygen or loss of hydrogenThe classical definition of oxidation includes both: gaining oxygen (e.g., 2Mg + O₂ → 2MgO) and losing hydrogen (e.g., H₂S → S + H₂, where H₂S loses hydrogen). The modern definition is loss of electrons, but the classical definitions are still widely taught, especially in inorganic chemistry.
Q36. Which of the following is an example of galvanisation?
Coating iron with zincGalvanization is the process of coating iron or steel with a layer of zinc to prevent rusting. Zinc is more reactive than iron, so it corrodes preferentially (sacrificial protection). Even if the zinc coating gets scratched, the exposed iron is still protected because zinc will corrode instead. This is commonly used for roofing sheets, buckets, and fence posts.
Q37. White substance formed on burning magnesium is:
MgO2Mg + O₂ → 2MgO. The white powder formed is magnesium oxide. It is a basic oxide that turns red litmus blue. MgO is also known as magnesia and has high melting point (2852°C), making it useful as a refractory material in furnace linings.
Q38. Which method is best to prevent rusting of iron gates?
All of theseThe question asks for the “best” method, but all listed methods are effective for different situations. For iron gates, painting is commonly used (aesthetic and protective). Oiling is for moving parts. Galvanization is best for long-term outdoor protection but is applied before fabrication. A combination (galvanized then painted) provides the best protection. All are valid prevention methods.
Q39. BaCl₂ + H₂SO₄ produces:
BaSO₄ + HClBaCl₂ + H₂SO₄ → BaSO₄ (white precipitate) + 2HCl. This is a double displacement reaction. Barium sulphate is insoluble in both water and acids, forming a dense white precipitate. This reaction is used in the laboratory test for sulphate ions: the formation of a white precipitate insoluble in dilute HCl confirms SO₄²⁻.
Q40. The process of eating away of metals by air, moisture, or chemicals is called:
CorrosionCorrosion is the gradual destruction of metals by chemical reactions with their environment. This includes reaction with air (oxygen), moisture (water), acids, salts, and other chemicals. While oxidation is often involved, corrosion is the broader, correct term. Examples include rusting of iron, tarnishing of silver, and patination of copper.
Q41. In the reaction Zn + CuSO₄ → ZnSO₄ + Cu, which substance is reduced?
CuSO₄In this reaction, copper in CuSO₄ goes from Cu²⁺ (oxidation state +2) to Cu⁰ (oxidation state 0). This is reduction (gain of electrons). The copper sulphate is the substance that gets reduced. Zn is oxidized (loses electrons to become Zn²⁺). The product Cu is the reduced form, but the question asks which substance is reduced — the reactant CuSO₄.
Q42. Iron corrodes due to attack of:
Moisture, acids etc.Rusting of iron requires both oxygen and water. But corrosion can be accelerated by acids (acid rain), salts (road salt in winter), and other pollutants. Pure dry oxygen does not cause rusting — water is essential. Similarly, pure water without dissolved oxygen does not cause rusting. Both moisture AND oxygen AND often other factors are involved.
Q43. Balanced equations follow law of:
Conservation of massThe Law of Conservation of Mass (Lavoisier, 1789) states that mass is neither created nor destroyed in a chemical reaction. Therefore, in a balanced chemical equation, the total mass of reactants equals the total mass of products. This requires that the number of atoms of each element is the same on both sides of the equation.
Q44. Rancidity affects:
Taste and smellRancidity primarily affects the organoleptic properties — taste and smell become unpleasant (bitter, metallic, or “off”). While colour may sometimes change slightly, and there can be minor weight changes due to oxygen uptake, the most noticeable and undesirable effects are on taste and smell. Rancid food is unpalatable and potentially harmful.
Q45. Barium chloride reacts with aluminum sulphate to form:
BaSO₄ precipitate3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄ (white precipitate) + 2AlCl₃. Barium sulphate is insoluble and forms a precipitate. While the complete answer includes AlCl₃, the question specifically asks what is formed, and the precipitate (BaSO₄) is the key observable product. This reaction is used to test for sulphate ions.
Q46. HNO₃ + Ca(OH)₂ produces:
Ca(NO₃)₂ + H₂O2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O. This is a neutralization reaction between nitric acid (acid) and calcium hydroxide (base). The products are calcium nitrate (salt) and water. Calcium nitrate is a soluble salt and remains in solution. This is a typical acid-base neutralization.
Q47. A balanced equation has:
Equal atoms on both sidesA balanced chemical equation has the same number of atoms of each element on both the reactant and product sides. This satisfies the Law of Conservation of Mass. The number of molecules may differ (e.g., 2H₂ + O₂ → 2H₂O has 3 molecules on left, 2 on right), but atoms are equal. Temperature and volume are not relevant to balancing.
Q48. A substance is oxidised if it:
Gains oxygenAccording to the classical definition of oxidation, a substance is oxidized when it gains oxygen. Example: 2Mg + O₂ → 2MgO (magnesium gains oxygen, so it is oxidized). Other definitions include loss of hydrogen or loss of electrons. Gaining water is not a definition of oxidation.
Q49. Black coating indicates:
OxidationBlack coating on silver (silver sulphide) forms due to oxidation of silver (though technically silver’s oxidation state increases, and silver ions combine with sulphide). Black coating on copper (copper oxide) forms when copper is heated in air — again an oxidation reaction. While these involve reduction of other species (oxygen or sulphur), the black coating formation on the metal is due to the metal being oxidized.
Q50. Fats become rancid due to:
OxidationRancidity is caused by the oxidation of unsaturated fats and oils. Atmospheric oxygen reacts with carbon-carbon double bonds in fatty acids, forming peroxides that break down into volatile aldehydes, ketones, and carboxylic acids. These compounds cause the characteristic unpleasant smell and taste. While hydrolysis can also spoil fats (hydrolytic rancidity), oxidative rancidity is the most common and the one referred to in most contexts.