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H2S gas when passed through a solution of cations containing HCl, precipitates the cations of second group of qualitative analysis but not those belonging to the fourth group. It is because

1. presence of HCl decreases the sulphide ion concentration.
2. solubility product of group II sulphides is more than that of group IV sulphides.
3. presence of HCl increases the sulphide ion concentration.
4. sulphides of group IV cations are unstable in HCl.

Correct answer: presence of HCl decreases the sulphide ion concentration.

Solution

In qualitative analysis, the presence of HCl suppresses the ionization of H2S, reducing the concentration of sulphide ions. This allows only the less soluble group II sulphides to precipitate, while group IV sulphides remain soluble.

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