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Question:

In which case change in entropy is negative?

Expansion of a gas at constant temperature

Evaporation of water

Sublimation of solid to gas

2H(g)→H2(g)

Solution:

Correct option is D. 2H(g)→H2(g)→H2O(l)⇌H2O(v), ΔS>0→Expansion of gas at a constant temperature, ΔS>0→Sublimation of solid to gas, ΔS>0→2H(g)→H2(g), ΔS<0 (∵Δng<0)