NDA Current Affairs | 13 Sep Exam
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Important Elements & Their Compounds – NDA Chemistry PYQs
Coastal States, Gulfs, Straits, Islands and Maritime Zones of India
Indian Geography • Coastal Geography • PYQs Included
NDA 2026-II
Q. 1. Consider the following statements regarding the properties of hydrogen and water :
I. Tritium, the isotope of hydrogen, is radioactive and emits low energy alpha particles.
II. In the gas phase, the structure of water is linear.
III. The basic principle of a hydrogen economy is the transportation and storage of energy in the form of liquid or gaseous molecular hydrogen.
Which of the statements given above is/are not correct ?
(a) I and II only
(b) II and III only
(c) I and III only
(d) II only
Answer: (a) I and II only
| Explanation: Statement I: Tritium is radioactive but emits beta particles (electrons), not alpha particles. Statement I is NOT correct. Statement II: Water in the gas phase (steam) has a bent/V-shaped structure (due to lone pairs on O), not linear. Statement II is NOT correct. Statement III: Correct – the hydrogen economy concept involves H₂ as an energy carrier. So I and II are not correct. Concept Tested: Properties of tritium (beta emitter) and water structure (bent) |
Q. 2. Consider the following statements :
I. A 30% solution of hydrogen peroxide is marketed as ’10 volume’ H₂O₂.
II. In the compound copper sulphate pentahydrate, all the five water molecules are hydrogen bonded.
Which of the statements given above is/are correct ?
(a) I only
(b) II only
(c) Both I and II
(d) Neither I nor II
Answer: (d) Neither I nor II
| Explanation: Statement I: “10 volume” H₂O₂ means 1 L of H₂O₂ releases 10 L of O₂ at STP – this corresponds to approximately 3% H₂O₂, not 30%. Statement I is incorrect. Statement II: In CuSO₄·5H₂O, four water molecules coordinate directly to Cu²⁺; only one is hydrogen-bonded to sulphate. Not all five are hydrogen bonded. Statement II is incorrect. Neither is correct. Concept Tested: Hydrogen peroxide “volume” concentration; water molecules in CuSO₄·5H₂O |
Q. 3. Consider the following statements :
I. The leaves of nettle, a herbaceous plant, cause painful stings when touched accidentally because of the secretion of formic acid.
II. When gypsum is heated at 100°C, it forms calcium carbonate hemihydrate, called Plaster of Paris.
III. When moistened with water, anhydrous copper sulphate forms a green-coloured copper sulphate dihydrate.
Which of the statements given above is/are correct ?
(a) I only
(b) III only
(c) II and III
(d) I and II
Answer: (a) I only
| Explanation: Statement I: Correct – nettle stings due to formic (methanoic) acid. Statement II: Incorrect – when gypsum (CaSO₄·2H₂O) is heated, it forms Plaster of Paris (CaSO₄·½H₂O), which is CALCIUM SULPHATE hemihydrate, not calcium carbonate hemihydrate. Statement III: Incorrect – anhydrous CuSO₄ is white; adding water forms CuSO₄·5H₂O which is BLUE, not green. Only Statement I is correct. Concept Tested: Nettle acid; Plaster of Paris formula; colour of CuSO₄·5H₂O |
NDA 2025-II
Q. 4. The reaction that occurs on passing carbon dioxide gas through lime water is
(a) CaCO₃ + H₂O + CO₂ → Ca(HCO₃)₂
(b) Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
(c) CaO + CO₂ → CaCO₃
(d) CaCl₂ + H₂O + CO₂ → CaCO₃ + 2HCl
Answer: (b) Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
| Explanation: Lime water is Ca(OH)₂ solution. Passing CO₂ makes it milky: Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O. Option (a) represents excess CO₂ (CaCO₃ dissolves back). Option (c) involves CaO, not lime water. Option (d) involves CaCl₂. Concept Tested: Lime water test for CO₂ – Ca(OH)₂ + CO₂ → CaCO₃ |
Q. 5. Which one of the following statements is NOT correct?
(a) Water of crystallization is the fixed number of water molecules present in one formula unit of a salt
(b) The molecular formula of Plaster of Paris is CaSO₄·2H₂O
(c) Washing soda is used for removing the permanent hardness of water
(d) The atmosphere of Venus is made up of thick white and yellow clouds of sulphuric acid
Answer: (b) The molecular formula of Plaster of Paris is CaSO₄·2H₂O
| Explanation: CaSO₄·2H₂O is the formula of GYPSUM, not Plaster of Paris. Plaster of Paris = CaSO₄·½H₂O. Options (a), (c), (d) are all correct. Concept Tested: Plaster of Paris formula – CaSO₄·½H₂O (not ·2H₂O) |
NDA 2025-I
Q. 6. Which one of the following oxides is a neutral oxide?
(a) CO
(b) CO₂
(c) Na₂O
(d) MgO
Answer: (a) CO
| Explanation: Carbon monoxide (CO) is a neutral oxide – it does not react with water, acid or base to form salts. CO₂ is an acidic oxide (forms H₂CO₃ with water). Na₂O is a basic oxide. MgO is also a basic oxide. Concept Tested: Neutral oxide – CO |
Q. 7. Match List I with List II and select the answer using the code given below the Lists:
List I (Chemical Name)
A. Washing soda
B. Baking soda
C. Bleaching powder
D. Gypsum
List II (Chemical Formula)
1. CaOCl₂
2. NaHCO₃
3. Na₂CO₃·10H₂O
4. CaSO₄·2H₂O
Code :
A B C D
(a) 4 2 1 3
(b) 4 1 2 3
(c) 3 1 2 4
(d) 3 2 1 4
(a) 4 2 1 3
(b) 4 1 2 3
(c) 3 1 2 4
(d) 3 2 1 4
Answer: (d) A-3, B-2, C-1, D-4
| Explanation: A. Washing soda → Na₂CO₃·10H₂O = 3. B. Baking soda → NaHCO₃ = 2. C. Bleaching powder → CaOCl₂ = 1. D. Gypsum → CaSO₄·2H₂O = 4. Code (d): A-3, B-2, C-1, D-4. Concept Tested: Matching common chemical names to formulas |
NDA 2024-I
Q. 8. Which among the following is the correct composition of Borax?
(a) Sodium, Boron, Magnesium and Hydrogen
(b) Sodium, Boron, Oxygen and Hydrogen
(c) Potassium, Boron, Oxygen and Hydrogen
(d) Sodium, Boron, Nitrogen and Hydrogen
Answer: (b) Sodium, Boron, Oxygen and Hydrogen
| Explanation: Borax is sodium tetraborate decahydrate: Na₂B₄O₇·10H₂O. Its elements are sodium (Na), boron (B), oxygen (O) and hydrogen (H from water). No magnesium, potassium or nitrogen. Concept Tested: Composition of borax – Na, B, O, H |
Q. 9. Which one among the following oxides has the highest melting point?
(a) Na₂O
(b) MgO
(c) Fe₂O₃
(d) CuO
Answer: (b) MgO
| Explanation: MgO (magnesium oxide) has one of the highest melting points among common metal oxides – approximately 2852 °C. It has a very stable ionic lattice. Na₂O melts at around 1275 °C. Fe₂O₃ at ~1565 °C. CuO at ~1326 °C. Concept Tested: High melting point oxide – MgO |
NDA 2023-I
Q. 10. Copper sulphate crystals available in the market are blue coloured crystals. By careful heating, they turn to white colour. Which one of the following is responsible for the blue colour ?
(a) Oxygen
(b) Nitrogen
(c) Water
(d) Hydrogen
Answer: (c) Water
| Explanation: The blue colour of CuSO₄·5H₂O is due to the 5 molecules of water of crystallisation. When heated, these water molecules are removed, leaving anhydrous CuSO₄ which is white. Adding water back restores the blue colour. Concept Tested: Blue colour of CuSO₄·5H₂O due to water of crystallisation |
NDA 2022-II
Q. 11. Which one of the following salts does not possess water of crystallization?
(a) Potassium permanganate
(b) Blue vitriol
(c) Washing soda
(d) Mohr’s salt
Answer: (a) Potassium permanganate
| Explanation: Potassium permanganate (KMnO₄) does not have water of crystallisation – it is an anhydrous salt. Blue vitriol = CuSO₄·5H₂O (5 water). Washing soda = Na₂CO₃·10H₂O (10 water). Mohr’s salt = (NH₄)₂Fe(SO₄)₂·6H₂O (6 water). Concept Tested: Salts without water of crystallisation – KMnO₄ |
NDA 2022-I
Q. 12. Which one of the following is the colour of hydrogen gas?
(a) Light yellow
(b) Orange
(c) Black
(d) Colourless
Answer: (d) Colourless
| Explanation: Hydrogen (H₂) is a colourless, odourless, and tasteless gas. It is the lightest of all gases. Concept Tested: Physical properties of H₂ – colourless gas |
NDA 2021-II
Q. 13. What is the number of water molecules present in a Ferrous Sulphate crystal?
(a) 1
(b) 3
(c) 5
(d) 7
Answer: (d) 7
| Explanation: Ferrous sulphate (FeSO₄·7H₂O), also called green vitriol or copperas, has 7 molecules of water of crystallisation. Concept Tested: Water of crystallisation in FeSO₄·7H₂O = 7 |
| ★ JOVIK Exam Insight: Blue vitriol = CuSO₄·5H₂O (5). Green vitriol = FeSO₄·7H₂O (7). White vitriol = ZnSO₄·7H₂O (7). |
Q. 14. What is the colour of the precipitate obtained by passing CO₂ gas through lime water?
(a) Green
(b) Blue
(c) White
(d) Brown
Answer: (c) White
| Explanation: CO₂ + Ca(OH)₂ → CaCO₃↓ + H₂O. Calcium carbonate (CaCO₃) precipitate is white. This is the standard lime water test for CO₂. Concept Tested: Lime water test for CO₂ – white precipitate of CaCO₃ |
Q. 15. Which one of the following is the chemical formula of Plaster of Paris?
(a) CaSO₄ · ½ H₂O
(b) CaSO₄ · 2 H₂O
(c) CaSO₄ · 5 H₂O
(d) CaSO₄ · 4 H₂O
Answer: (a) CaSO₄ · ½ H₂O
| Explanation: Plaster of Paris = CaSO₄·½H₂O (calcium sulphate hemihydrate). It is made by heating gypsum (CaSO₄·2H₂O) at 120–180°C. CaSO₄·2H₂O is gypsum. Concept Tested: Plaster of Paris formula – CaSO₄·½H₂O |
NDA 2021-I
Q. 16. Which one of the following statements about dihydrogen (H₂) is not correct?
(a) H₂ is lighter than air and insoluble in water.
(b) H₂ is inert at room temperature due to high H – H bond dissociation enthalpy.
(c) H₂ reacts with alkali metals at high temperature to yield metal hydrides.
(d) A mixture of NO₂ and H₂ is known as Syngas.
Answer: (d) A mixture of NO₂ and H₂ is known as Syngas.
| Explanation: Syngas (synthesis gas) is a mixture of CO and H₂, not NO₂ and H₂. Options (a), (b) and (c) are all correct properties of dihydrogen. Concept Tested: Properties of H₂ – syngas = CO + H₂ (not NO₂ + H₂) |
Q. 17. Common salt (NaCl) is not used as a raw material for preparation of which one of the following compounds?
(a) Bleaching powder
(b) Baking soda
(c) Plaster of Paris
(d) Washing soda
Answer: (c) Plaster of Paris
| Explanation: Plaster of Paris (CaSO₄·½H₂O) is made by heating gypsum (CaSO₄·2H₂O) – it does not require NaCl. Bleaching powder (CaOCl₂) involves Cl₂ (from NaCl electrolysis). Baking soda (NaHCO₃) involves Na (from NaCl via Solvay process). Washing soda (Na₂CO₃) is made via the Solvay process using NaCl. Concept Tested: NaCl not used in Plaster of Paris manufacture |
Q. 18. At nearly 70°C, sodium bicarbonate shows the property of gradually decomposing, which makes it usable in bakery products. The product of decomposition responsible for this use of sodium bicarbonate is
(a) Carbon dioxide
(b) Hydrogen
(c) Water vapour
(d) Oxygen
Answer: (a) Carbon dioxide
| Explanation: Same as NDA 2020 Q143. 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂. CO₂ gas causes dough to rise. Concept Tested: Baking soda decomposition – CO₂ leavening (repeated) |
Q. 19. Number of molecules of water of crystallization in copper sulphate, sodium carbonate and Gypsum are
(a) 5, 10 and 2 respectively
(b) 10, 2 and 5 respectively
(c) 5, 2 and 10 respectively
(d) 2, 5 and 10 respectively
Answer: (a) 5, 10 and 2 respectively
| Explanation: Same as NDA 2020 Q144. CuSO₄·5H₂O = 5, Na₂CO₃·10H₂O = 10, CaSO₄·2H₂O = 2. Concept Tested: Water of crystallisation numbers (repeated question) |
Q. 20. Which one of the following is the best example of desiccant?
(a) Silica gel
(b) Polystyrene
(c) Sodium chloride
(d) Sodium carbonate
Answer: (a) Silica gel
| Explanation: Same as NDA 2020 Q147. Silica gel is the best desiccant. Concept Tested: Desiccant = silica gel (repeated) |
NDA 2020
Q. 21. Chalk and marble are different forms of
(a) Calcium hydrogen carbonate
(b) Calcium carbonate
(c) Calcium acetate
(d) Sodium carbonate
Answer: (b) Calcium carbonate
| Explanation: Both chalk and marble are naturally occurring forms of calcium carbonate (CaCO₃). Chalk is a soft, porous form. Marble is a hard, crystalline metamorphic rock. Limestone is also CaCO₃. Concept Tested: Natural forms of CaCO₃ – chalk and marble |
Q. 22. A very large volume of hydrogen can be accommodated by making
(a) non-metallic hydrides.
(b) hydrogen peroxide.
(c) non-stoichiometric hydrides.
(d) alkali metal hydrides.
Answer: (c) non-stoichiometric hydrides.
| Explanation: Same question as NDA 2019-II Q88. Non-stoichiometric hydrides formed by transition metals can store large volumes of hydrogen. This repeated appearance confirms it is a high-frequency concept. Concept Tested: Hydrogen storage – non-stoichiometric hydrides (repeated) |
Q. 23. At nearly 70°C, sodium bicarbonate shows the property of gradually decomposing, which makes it usable in bakery products. The product of decomposition responsible for this use of sodium bicarbonate is
(a) Carbon dioxide
(b) Hydrogen
(c) Water vapour
(d) Oxygen
Answer: (a) Carbon dioxide
| Explanation: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂. The CO₂ gas released causes dough to rise (leavening action). Water vapour is also produced but CO₂ is primarily responsible for the leavening effect. Concept Tested: Baking soda in bakery – CO₂ produced on decomposition |
Q. 24. Number of molecules of water of crystallization in copper sulphate, sodium carbonate and Gypsum are
(a) 5, 10 and 2 respectively
(b) 10, 2 and 5 respectively
(c) 5, 2 and 10 respectively
(d) 2, 5 and 10 respectively
Answer: (a) 5, 10 and 2 respectively
| Explanation: CuSO₄·5H₂O (blue vitriol) = 5 water molecules. Na₂CO₃·10H₂O (washing soda) = 10 water molecules. CaSO₄·2H₂O (gypsum) = 2 water molecules. Order: 5, 10, 2. Concept Tested: Water of crystallisation – CuSO₄ (5), Na₂CO₃ (10), gypsum (2) |
| ★ JOVIK Exam Insight: These three compounds and their water of crystallisation numbers are a classic NDA recurring question. Learn: CuSO₄ = 5, Na₂CO₃ = 10, gypsum = 2, FeSO₄ = 7. |
Q. 25. Which one of the following is the best example of desiccant?
(a) Silica gel
(b) Polystyrene
(c) Sodium chloride
(d) Sodium carbonate
Answer: (a) Silica gel
| Explanation: A desiccant is a substance that absorbs moisture. Silica gel (SiO₂·nH₂O) is one of the most effective and widely used desiccants – found in packets inside packaging to keep products dry. Polystyrene, NaCl and Na₂CO₃ are not desiccants. Concept Tested: Desiccant – silica gel absorbs moisture |
NDA 2019-II
Q. 26. Which one of the following does not represent the salt, Calcium carbonate?
(a) Lime water
(b) Limestone
(c) Chalk
(d) Marble
Answer: (a) Lime water
| Explanation: Lime water is an aqueous solution of calcium hydroxide, Ca(OH)₂ – not calcium carbonate. Limestone, chalk and marble are all forms of calcium carbonate (CaCO₃). Concept Tested: Forms of CaCO₃ – limestone, chalk, marble. Lime water = Ca(OH)₂ |
Q. 27. A very large volume of hydrogen can be accommodated by making
(a) non-metallic hydrides.
(b) hydrogen peroxide.
(c) non-stoichiometric hydrides.
(d) alkali metal hydrides.
Answer: (c) non-stoichiometric hydrides.
| Explanation: Non-stoichiometric (interstitial) hydrides are formed by transition metals that absorb large amounts of hydrogen into their lattice. They can accommodate very large volumes of H₂. This property is used in hydrogen storage for fuel cell technology. Concept Tested: Hydrogen storage – non-stoichiometric (interstitial) hydrides |
NDA 2019-I
Q. 28. Which one of the following will NOT produce carbon dioxide on reacting with an aqueous solution of hydrochloric acid?
(a) Limestone
(b) Quick Lime
(c) Chalk
(d) Marble
Answer: (b) Quick Lime
| Explanation: Quick lime = CaO (calcium oxide). CaO + 2HCl → CaCl₂ + H₂O. No CO₂ is produced. Limestone (CaCO₃), chalk (CaCO₃) and marble (CaCO₃) all produce CO₂ with HCl: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑. Concept Tested: Reaction with HCl – CaO does not produce CO₂ |
| ★ JOVIK Exam Insight: Quick lime = CaO (no carbon, no CO₂ with acid). Limestone = chalk = marble = CaCO₃ (all produce CO₂). |
Q. 29. Tooth enamel is made up of which one of the following calcium compounds?
(a) Calcium carbonate
(b) Calcium sulphate
(c) Calcium hydroxide
(d) Calcium phosphate
Answer: (d) Calcium phosphate
| Explanation: Tooth enamel is mainly hydroxyapatite: Ca₁₀(PO₄)₆(OH)₂ – a form of calcium phosphate. It is the hardest substance in the human body. Concept Tested: Tooth enamel – calcium phosphate (hydroxyapatite) |
NDA 2018-II
Q. 30. Which one of the following is the chemical formula of gypsum?
(a) CaSO₄·2H₂O
(b) Ca₂SiO₄
(c) 2CaSO₄·H₂O
(d) CaSO₄
Answer: (a) CaSO₄·2H₂O
| Explanation: Gypsum = CaSO₄·2H₂O (calcium sulphate dihydrate). Plaster of Paris = CaSO₄·½H₂O. Option (c) represents two formula units of Plaster of Paris. Option (d) is anhydrous calcium sulphate. Concept Tested: Gypsum formula – CaSO₄·2H₂O (repeated) |
NDA 2018-I
Q. 31. Brine is an aqueous solution of
(a) NaCl
(b) NaOH
(c) NaHCO₃
(d) Na₂CO₃
Answer: (a) NaCl
| Explanation: Brine is a concentrated aqueous solution of sodium chloride (NaCl – common salt). It is used in the chlor-alkali industry and food preservation. Concept Tested: Brine = concentrated NaCl solution |
Q. 32. Which one of the following is the chemical formula of Washing Soda?
(a) NaHCO₃
(b) Na₂CO₃·10H₂O
(c) Na₂CO₃·5H₂O
(d) NaOH
Answer: (b) Na₂CO₃·10H₂O
| Explanation: Washing soda is sodium carbonate decahydrate: Na₂CO₃·10H₂O. It has 10 molecules of water of crystallisation. NaHCO₃ is baking soda. Concept Tested: Washing soda formula – Na₂CO₃·10H₂O with 10 water molecules |
Q. 33. Which one of the following is NOT true for bleaching powder?
(a) It is used as a reducing agent in chemical industries
(b) It is used for bleaching wood pulp in paper factories
(c) It is used for disinfecting drinking water
(d) It is used for bleaching linen in textile industry
Answer: (a) It is used as a reducing agent in chemical industries
| Explanation: Bleaching powder (CaOCl₂) is an OXIDISING agent, not a reducing agent. It bleaches through oxidation – releasing chlorine, which oxidises and removes colour. Options (b), (c) and (d) are all correct uses of bleaching powder. Concept Tested: Bleaching powder – oxidising agent, not reducing agent |
Q. 34. Which one of the following is the number of water molecules that share with two formula unit CaSO₄ in plaster of Paris?
(a) One
(b) Two
(c) Five
(d) Ten
Answer: (a) One
| Explanation: Plaster of Paris is (CaSO₄)₂·H₂O or CaSO₄·½H₂O. For two formula units of CaSO₄, there is ONE shared water molecule. So two CaSO₄ share one H₂O. Concept Tested: Plaster of Paris – CaSO₄·½H₂O water molecules per formula unit |
NDA 2017-II
Q. 35. Which one among the following chemicals is used as washing soda?
(a) Calcium carbonate
(b) Calcium bicarbonate
(c) Sodium carbonate
(d) Sodium bicarbonate
Answer: (c) Sodium carbonate
| Explanation: Washing soda = Na₂CO₃·10H₂O (sodium carbonate decahydrate). Sodium bicarbonate (NaHCO₃) is baking soda. Calcium carbonate is chalk/limestone. Concept Tested: Washing soda = sodium carbonate (repeated) |
NDA 2017-I
Q. 36. The chemical name of baking soda is
(a) Na₂CO₃
(b) NaHCO₃
(c) CaCO₃
(d) NaOH
Answer: (b) NaHCO₃
| Explanation: Baking soda = NaHCO₃ (sodium hydrogen carbonate). Na₂CO₃ is washing soda. CaCO₃ is chalk/limestone. NaOH is caustic soda. Concept Tested: Baking soda chemical formula – NaHCO₃ (repeated) |
NDA 2016-I
Q. 37. Which one of the following is the chemical name for baking soda ?
(a) Sodium bicarbonate (Sodium hydrogen carbonate)
(b) Sodium carbonate
(c) Potassium bicarbonate (Potassium hydrogen carbonate)
(d) Potassium carbonate
Answer: (a) Sodium bicarbonate (Sodium hydrogen carbonate)
| Explanation: Baking soda = NaHCO₃ = sodium bicarbonate = sodium hydrogen carbonate. It releases CO₂ on heating or with acid, causing dough to rise. Sodium carbonate is washing soda. Concept Tested: Baking soda = NaHCO₃ = sodium bicarbonate |
Q. 38. Which one of the following oxides dissolves in water ?
(a) CuO
(b) Al₂O₃
(c) Fe₂O₃
(d) Na₂O
Answer: (d) Na₂O
| Explanation: Na₂O (sodium oxide) dissolves in water to form NaOH: Na₂O + H₂O → 2NaOH. CuO, Al₂O₃ and Fe₂O₃ are insoluble in water under normal conditions. Concept Tested: Metal oxide dissolving in water – Na₂O forms NaOH |
NDA 2015-II
Q. 39. The symbol of the element ‘Tungsten’ is:
(a) Ta
(b) W
(c) Tl
(d) Tc
Answer: (b) W
| Explanation: The symbol for Tungsten is W, from its German name Wolfram. Tungsten has the highest melting point of all metals (3422 °C). Ta is Tantalum, Tl is Thallium, Tc is Technetium. Concept Tested: Chemical symbol of Tungsten – W (Wolfram) |
NDA 2015-I
Q. 40. Washing Soda is the common name for
(a) Calcium Carbonate
(b) Magnesium Carbonate
(c) Sodium Carbonate
(d) Potassium Carbonate
Answer: (c) Sodium Carbonate
| Explanation: Washing soda is sodium carbonate decahydrate: Na₂CO₃·10H₂O. It is used in cleaning, water softening, and manufacturing. Baking soda is NaHCO₃. Calcium carbonate is chalk/limestone. Concept Tested: Washing soda = sodium carbonate (Na₂CO₃) |
| ★ JOVIK Exam Insight: Common names: Washing soda = Na₂CO₃·10H₂O. Baking soda = NaHCO₃. Plaster of Paris = CaSO₄·½H₂O. Gypsum = CaSO₄·2H₂O. Blue vitriol = CuSO₄·5H₂O. |
NDA 2014-II
Q. 41. A sample of gas is to be identified by means of its behaviour in the presence of a glowing splint. Which of the following gases will neither itself burn nor cause the splint to burn?
(a) Oxygen
(b) Nitrogen
(c) Hydrogen
(d) Methane
Answer: (b) Nitrogen
| Explanation: Oxygen relights a glowing splint. Hydrogen and methane burn (they are combustible). Nitrogen is an inert gas – it neither burns nor supports combustion. A glowing splint goes out in nitrogen. Concept Tested: Gas identification by splint test – nitrogen is inert |
NDA 2014-I
Q. 42. Which of the following statements about hydrogen is/are correct?
1. Hydrogen has three isotopes of which protium is the most common.
2. Hydrogen ion (H⁺) exists freely in solution.
3. Dihydrogen, H₂, acts as a reducing agent.
Select the correct answer using the code given below.
(a) 1, 2 and 3
(b) 1 only
(c) 1 and 3 only
(d) 3 only
Answer: (c) 1 and 3 only
| Explanation: Statement 1 is correct: hydrogen has three isotopes – protium (¹H, most common), deuterium (²H) and tritium (³H). Statement 2 is incorrect: H⁺ does not exist freely in solution; it is always hydrated as H₃O⁺ (hydronium ion). Statement 3 is correct: H₂ acts as a reducing agent in many reactions. Concept Tested: Properties of hydrogen – isotopes, H⁺ in solution, reducing nature |
NDA 2013-II
Q. 43. Statement I: Limestone decomposes when it is heated in air. Statement II: Increase in the content of CO₂ in the atmosphere in recent years is mainly due to the using of limestone in the manufacture of cement.
(a) Both the statements are individually true and Statement II is the correct explanation of Statement I
(b) Both the statements are individually true but Statement II is not the correct explanation of Statement I
(c) Statement I is true but Statement II is false
(d) Statement I is false but Statement II is true
Answer: (b) Both the statements are individually true but Statement II is not the correct explanation of Statement I
| Explanation: Statement I is correct: CaCO₃ → CaO + CO₂ on heating (calcination). Statement II is also correct – cement manufacture releases CO₂. However, Statement II does not explain Statement I (Statement I is about a chemical reaction; Statement II is about an atmospheric consequence). They are both true but II does not explain I. Concept Tested: Decomposition of limestone; CO₂ release in cement production |
Q. 44. Two reactants in a flask produce bubbles of gas; it turns lime water into milky. The reactants in the flask are
(a) Zinc and hydrochloric acid
(b) Magnesium carbonate and hydrochloric acid
(c) Magnesium nitrate and hydrochloric acid
(d) Magnesium sulphate and hydrochloric acid
Answer: (b) Magnesium carbonate and hydrochloric acid
| Explanation: A gas that turns lime water milky is CO₂. MgCO₃ + 2HCl → MgCl₂ + H₂O + CO₂↑. The CO₂ makes the lime water milky (CaCO₃ precipitate forms). Zinc + HCl produces H₂, not CO₂. Mg(NO₃)₂ and MgSO₄ do not produce CO₂ with HCl. Concept Tested: Gas test – CO₂ turns lime water milky |
NDA 2013-I
Q. 45. Which one among the following is the chemical formula of gypsum which is an ingredient of cement?
(a) Ca₂SiO₄
(b) CaSO₄·2H₂O
(c) CaO
(d) CaSO₄·3H₂O
Answer: (b) CaSO₄·2H₂O
| Explanation: Gypsum is calcium sulphate dihydrate: CaSO₄·2H₂O. It is added to cement to control the setting time. Ca₂SiO₄ is dicalcium silicate (a component of cement itself). CaO is quicklime. Concept Tested: Gypsum formula – CaSO₄·2H₂O |
| ★ JOVIK Exam Insight: Gypsum = CaSO₄·2H₂O. Plaster of Paris = CaSO₄·½H₂O. Both are calcium sulphate but with different water content. NDA tests both. |
NDA 2012-II
Q. 46. Match List I with List II and select the correct answer using the code given below the Lists:
List I (Compound)
A. Cellulose nitrate
B. Potassium sulphate
C. Potassium salt of fatty acids
D. Calcium oxide
List II (Use)
1. Soft soap
2. Gun powder
3. Fertilizer
4. Glass
Code :
A B C D
(a) 2 3 1 4
(b) 2 1 3 4
(c) 4 1 3 2
(d) 4 3 1 2
(a) 2 3 1 4
(b) 2 1 3 4
(c) 4 1 3 2
(d) 4 3 1 2
Answer: (a) A-2, B-3, C-1, D-4
| Explanation: A. Cellulose nitrate (gun cotton) → 2. Gun powder/explosive. B. Potassium sulphate (K₂SO₄) → 3. Fertilizer. C. Potassium salt of fatty acids (potassium soap) → 1. Soft soap. D. Calcium oxide (CaO, quicklime) → 4. Glass (ingredient in glass making). Code (a): A-2, B-3, C-1, D-4. Concept Tested: Uses of compounds – cellulose nitrate, K₂SO₄, potassium soap, CaO |
NDA 2012-I
Q. 47. Statement I: The blue colour of copper sulphate crystal disappears when it is heated strongly. Statement II: Due to heating, water of crystallization of crystal is lost.
(a) Both the statements are individually true and Statement II is the correct explanation of Statement I
(b) Both the statements are individually true but Statement II is not the correct explanation of Statement I
(c) Statement I is true but Statement II is false
(d) Statement I is false but Statement II is true
Answer: (a) Both the statements are individually true and Statement II is the correct explanation of Statement I
| Explanation: CuSO₄·5H₂O (blue vitriol) is blue due to the 5 water molecules of crystallisation. When heated, these water molecules are driven off, leaving anhydrous CuSO₄ which is white. Statement II directly and correctly explains Statement I. Concept Tested: Water of crystallisation – CuSO₄·5H₂O turns white on heating |
NDA 2011-II
Q. 48. The metal constituent of chlorophyll is
(a) Iron
(b) Potassium
(c) Manganese
(d) Magnesium
Answer: (d) Magnesium
| Explanation: Chlorophyll, the green pigment in plants responsible for photosynthesis, has magnesium (Mg) as its central metal ion. This is analogous to haemoglobin, which has iron (Fe) as its central metal. Concept Tested: Metal in chlorophyll – magnesium |
| ★ JOVIK Exam Insight: Chlorophyll = Magnesium. Haemoglobin = Iron. Vitamin B₁₂ = Cobalt. NDA tests all three. |
NDA 2009-I
Q. 49. The metal compound commonly found in Sindhoor or Kumkum is based on
(a) Tin
(b) Lead
(c) Copper
(d) Zinc
Answer: (b) Lead
| Explanation: Traditional Sindhoor (vermilion) is based on lead sulphide (PbS) or lead oxide (Pb₃O₄/red lead), though modern versions may use safer alternatives. The traditional compound uses lead as the metal base. Note: modern non-toxic Sindhoor uses turmeric or safer dyes. Concept Tested: Traditional Sindhoor – lead-based compound |
Q. 50. Alum is used as
(a) an analgesic
(b) a fertilizer
(c) a disinfectant
(d) a purifier for water
Answer: (d) a purifier for water
| Explanation: Alum (K₂SO₄·Al₂(SO₄)₃·24H₂O or KAl(SO₄)₂·12H₂O) is added to turbid water. Al³⁺ ions hydrolyse to form Al(OH)₃ colloid, which coagulates suspended impurities and settles them down. This purifies water. Concept Tested: Alum as water purifier – coagulation of impurities |
| ★ JOVIK Exam Insight: Alum = water purifier. This fact appears in both chemistry and general science NDA questions. |