MCQ practice · SSC Chemistry Board questions · Chapter 7: Chemical Reactions
The gas 'X' in A is-
- i. CO₂
- ii. acidic
- iii. heavier than air
Think it through first, then pick an option.
- a i and ii
- b i and iii
- c ii and iii
- d i, ii and iii
Answer and explanation
Correct answer: d i, ii and iii
CaCO₃ → CaO + CO₂, so X is CO₂; it is acidic and heavier than air. All three are true.
Why the other options are wrong
- a i and ii: iii is also true: CO₂ has molar mass 44 against about 29 for air, so it is heavier than air.
- b i and iii: ii is left out: CO₂ dissolves in water to give carbonic acid, so it is acidic.
- c ii and iii: i is left out: CaCO₃ breaks down on heating into CaO and CO₂, so X = CO₂.
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