A yellow precipitate formed by $H X_{2} S$ in dilute $HCl$ is insoluble in yellow ammonium sulphide but dissolves in hot concentrated $HCl$ . Its cation gives a colourless solution with excess $NH X_{3}$ . The precipitate and the number of unpaired electrons in the cation in the ammine complex are

Answer: A

Insolubility in yellow ammonium sulphide rules out

As X_{2} S X_{3}

and

SnS X_{2}

(group IIB), and the yellow colour with the colourless ammine points to

CdS

and

[Cd (NH X_{3}) X_{4}] X^{2 +}

Cd X^{2 +}

d^{10}

, so it has no unpaired electrons and the complex is colourless and diamagnetic.