Elements and Compounds — GK Questions with Answers

1. Which of these non-metals conducts electricity?
   1. Sulphur
   2. Graphite
   3. Phosphorus
   4. Iodine
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   Answer: (B) Graphite

   In the layers of graphite one electron of each carbon stays free, so it conducts electricity.

2. Why is sodium kept in kerosene?
   1. It is heavy
   2. It changes colour
   3. It melts
   4. It reacts fast with air and moisture and catches fire
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   Answer: (D) It reacts fast with air and moisture and catches fire

   Sodium is extremely reactive — it flares up with oxygen and moisture of air; kerosene protects it.

3. Which metal does not release hydrogen from dilute HCl?
   1. Copper
   2. Magnesium
   3. Iron
   4. Zinc
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   Answer: (A) Copper

   Copper is below hydrogen in the reactivity series, so it cannot reduce H⁺.

4. Aqua regia is a mixture of —
   1. 3 parts HNO₃ + 1 part HCl
   2. HCl + H₂SO₄
   3. 3 parts HCl + 1 part HNO₃
   4. HNO₃ + H₂SO₄
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   Answer: (C) 3 parts HCl + 1 part HNO₃

   Conc. HCl and HNO₃ in a 3 : 1 ratio — it dissolves gold and platinum.

5. Which of these is highest in the reactivity series?
   1. Zinc
   2. Iron
   3. Magnesium
   4. Lead
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   Answer: (C) Magnesium

   Order: K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb — among these Mg is the most reactive.

6. What is made by the Solvay process?
   1. Sodium carbonate
   2. Caustic soda
   3. Bleaching powder
   4. Sulphuric acid
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   Answer: (A) Sodium carbonate

   From salt, ammonia and CO₂, first NaHCO₃ and then, on heating, Na₂CO₃ (soda ash) form.

7. Why does plaster of Paris become hard on adding water?
   1. It dries
   2. It is oxidised
   3. It absorbs CO₂
   4. It turns back into gypsum (CaSO₄·2H₂O)
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   Answer: (D) It turns back into gypsum (CaSO₄·2H₂O)

   CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O — gypsum crystals interlock into a hard solid.

8. By which reaction is bleaching powder made?
   1. CaO + Cl₂
   2. Ca(OH)₂ + Cl₂
   3. CaCO₃ + Cl₂
   4. NaOH + Cl₂
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   Answer: (B) Ca(OH)₂ + Cl₂

   Chlorine over dry slaked lime: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O; NaOH + Cl₂ gives household bleach (NaOCl).

9. Why is gypsum added to cement?
   1. To slow the setting
   2. For colour
   3. To reduce hardness
   4. To make it cheaper
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   Answer: (A) To slow the setting

   Gypsum slows the fast setting of tricalcium aluminate so there is time to work.

10. Sulphide ores are mainly concentrated by —
    1. magnetic separation
    2. hydraulic washing
    3. froth flotation
    4. leaching
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    Answer: (C) froth flotation

    Sulphide particles get wetted by pine oil and float up with the froth, gangue gets wetted by water and sinks.

11. Heating a carbonate ore in the absence of air is called —
    1. roasting
    2. calcination
    3. smelting
    4. liquation
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    Answer: (B) calcination

    In calcination CO₂ and moisture leave (ZnCO₃ → ZnO + CO₂); heating a sulphide in air is roasting.

12. Which reaction is used to join rail tracks?
    1. Haber
    2. Solvay
    3. Contact
    4. Thermite
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    Answer: (D) Thermite

    Fe₂O₃ + 2Al → 2Fe + Al₂O₃ — so much heat is released that iron melts and fills the gap.

13. Which compound forms in the Mond process of refining nickel?
    1. NiO
    2. NiSO₄
    3. NiCl₂
    4. Ni(CO)₄
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    Answer: (D) Ni(CO)₄

    Ni + 4CO → Ni(CO)₄ (volatile, ≈ 330–350 K), which breaks at ≈ 450–470 K to give pure nickel.

14. The main reducing agent of iron oxide in the blast furnace is —
    1. coke (C)
    2. carbon monoxide
    3. limestone
    4. hydrogen
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    Answer: (B) carbon monoxide

    Coke burns to CO₂ and then CO; Fe₂O₃ + 3CO → 2Fe + 3CO₂ is the main reduction.

15. Role of cryolite in the extraction of aluminium?
    1. Reducing agent
    2. Forming slag as flux
    3. Lowering the melting point of alumina and raising conductivity
    4. Catalyst
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    Answer: (C) Lowering the melting point of alumina and raising conductivity

    Pure Al₂O₃ melts at ≈ 2050 °C; dissolved in molten cryolite it can be electrolysed at ≈ 900 °C.

16. Which metal is not in German silver?
    1. Silver
    2. Zinc
    3. Nickel
    4. Copper
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    Answer: (A) Silver

    German silver = Cu + Zn + Ni; only its colour is like silver, it has no silver at all.

17. Bronze is made of which metals?
    1. Copper + zinc
    2. Copper + tin
    3. Iron + carbon
    4. Tin + lead
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    Answer: (B) Copper + tin

    Bronze = Cu + Sn; brass = Cu + Zn; solder = Sn + Pb.

18. What is needed for iron to rust?
    1. Only oxygen
    2. Only water
    3. Carbon dioxide
    4. Both oxygen and water
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    Answer: (D) Both oxygen and water

    From the three test-tube experiment — no rust in only dry air or only boiled water.

19. What is coated on iron in galvanising?
    1. Zinc
    2. Tin
    3. Chromium
    4. Nickel
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    Answer: (A) Zinc

    Zinc is more reactive than iron, so even when scratched it corrodes first and saves the iron.

20. Special property of borosilicate (Pyrex) glass?
    1. Very colourful
    2. Very soft
    3. Expands very little with heat
    4. Dissolves in water
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    Answer: (C) Expands very little with heat

    Because of low expansion it does not crack on sudden heating or cooling — ovenware and lab vessels.

21. Why is diamond an insulator?
    1. It is transparent
    2. It has no metal
    3. All four electrons of each carbon are used in σ bonds
    4. It is very hard
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    Answer: (C) All four electrons of each carbon are used in σ bonds

    In diamond each C is sp³-bonded to four C — no free electrons; in graphite one electron stays free.

22. Why is carbon monoxide poisonous?
    1. It binds strongly to haemoglobin and stops oxygen transport
    2. It is acidic
    3. It burns the lungs
    4. It is radioactive
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    Answer: (A) It binds strongly to haemoglobin and stops oxygen transport

    CO binds to haemoglobin hundreds of times more strongly than O₂ and forms carboxyhaemoglobin.

23. Correct conditions for making ammonia by the Haber process?
    1. V₂O₅, 2 bar
    2. Ni, 473 K
    3. Pt, 500 K
    4. Iron, ≈ 700 K, ≈ 200 atm
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    Answer: (D) Iron, ≈ 700 K, ≈ 200 atm

    N₂ + 3H₂ ⇌ 2NH₃ is exothermic and moles decrease — high pressure, a compromise temperature and an iron catalyst.

24. Chemical formula of laughing gas?
    1. NO
    2. N₂O
    3. NO₂
    4. N₂O₅
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    Answer: (B) N₂O

    Nitrous oxide (N₂O) — forms on heating NH₄NO₃; an anaesthetic.

25. Why is SO₃ not dissolved directly in water in the Contact process?
    1. A dense acid mist forms that does not condense
    2. There is no reaction
    3. It explodes
    4. SO₃ escapes
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    Answer: (A) A dense acid mist forms that does not condense

    The very exothermic reaction forms a mist of fine acid drops; so it is absorbed in 98% H₂SO₄ to make oleum.

26. Conc. H₂SO₄ turns sugar black — because of which property?
    1. Oxidising
    2. Acidic
    3. Dehydrating
    4. Reducing
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    Answer: (C) Dehydrating

    It pulls water (H and O) out of C₁₂H₂₂O₁₁ and leaves only carbon.

27. What harms the ozone layer the most?
    1. CO₂
    2. CFCs
    3. N₂
    4. Methane
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    Answer: (B) CFCs

    UV breaks CFCs into chlorine atoms that break thousands of ozone molecules; the Montreal Protocol (1987) ended them.

28. What causes the bleaching action of chlorine?
    1. Reduction
    2. Dehydration
    3. Acidity
    4. Oxidation by nascent oxygen
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    Answer: (D) Oxidation by nascent oxygen

    Cl₂ + H₂O → HCl + HOCl; the [O] from HOCl oxidises the coloured substance to a colourless one — permanent bleaching.

29. Which gas caused the Bhopal gas tragedy (1984)?
    1. Phosgene
    2. Ammonia
    3. Chlorine
    4. Methyl isocyanate
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    Answer: (D) Methyl isocyanate

    Methyl isocyanate (CH₃NCO) leaked from the Union Carbide plant on the night of 2–3 December 1984.

30. By the Lewis theory, which of these is an acid?
    1. NH₃
    2. BF₃
    3. H₂O
    4. OH⁻
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    Answer: (B) BF₃

    Boron in BF₃ has an incomplete octet — it can take an electron pair; NH₃, H₂O, OH⁻ are electron-pair donors (bases).

31. Colour of phenolphthalein in a basic solution?
    1. Colourless
    2. Yellow
    3. Pink
    4. Red
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    Answer: (C) Pink

    Phenolphthalein is colourless in acid and neutral, pink in base (above pH ≈ 8.3).

32. Why is baking soda applied on a bee sting?
    1. To neutralise the acid of the sting
    2. For cooling
    3. To stop bleeding
    4. To spread infection
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    Answer: (A) To neutralise the acid of the sting

    The sting has an acidic substance like formic acid; the weak base NaHCO₃ neutralises it.

33. Normal pH of human blood?
    1. 6.4
    2. 7.4
    3. 7.0
    4. 8.4
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    Answer: (B) 7.4

    Blood pH stays between 7.35 and 7.45 because of the H₂CO₃/HCO₃⁻ buffer.

34. The aqueous solution of which salt is basic?
    1. NaCl
    2. NH₄Cl
    3. CuSO₄
    4. Na₂CO₃
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    Answer: (D) Na₂CO₃

    Na₂CO₃ is a salt of a weak acid (H₂CO₃) and a strong base (NaOH) — hydrolysis increases OH⁻.

35. Formula of blue vitriol?
    1. CuSO₄·5H₂O
    2. FeSO₄·7H₂O
    3. ZnSO₄·7H₂O
    4. MgSO₄·7H₂O
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    Answer: (A) CuSO₄·5H₂O

    CuSO₄·5H₂O; green vitriol FeSO₄·7H₂O, white vitriol ZnSO₄·7H₂O, Epsom MgSO₄·7H₂O.

36. Oxidation state of iron in K₄[Fe(CN)₆]?
    1. +3
    2. 0
    3. +2
    4. +6
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    Answer: (C) +2

    4(+1) + x + 6(−1) = 0 → x = +2; +3 in K₃[Fe(CN)₆].

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