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Question:

When a substance 'A' reacts with water, it produces a combustible gas 'B' and a solution of substance 'C' in water. While another substance 'D' reacts with a solution of 'C' to produce the same gas B on warming, while 'D' can produce gas 'B' on reaction with dilute H₂SO₄ at room temperature. 'A' imparts a deep golden yellow colour to a smokeless flame on a Bunsen burner. Identify 'A', 'B', 'C', and 'D' respectively.

K,H2,KOH,Al

Na,H2,NaOH,Zn

Ca,H2,Ca(OH)2,Sn

CaC2,C2H2,Ca(OH2,F

Solution:

Correct option is B. Na,H2,NaOH,Zn
When Na reacts with water, it produces a combustible gas H₂ and a solution of NaOH in water.
Na + 2H₂O (g) → 2NaOH↓+H₂↑
When Zn reacts with this solution of NaOH, it also produces the same gas H₂ on warming but Zn can produce gas H₂ on reaction with dilute sulphuric acid at room temperature.
Zn +2 NaOH → Na₂ZnO₂↓+H₂↑
Zn +dilH₂SO₄ → ZnSO₄↓+H₂↑