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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3qc108

Select the correct statements about the group IV separation.

AAmmonia consumes $H X^{+}$ from $H X_{2} S$ and so raises $[S X^{2 -}]$
B $NiS$ and $CoS$ are black and do not dissolve in cold dilute $HCl$ after ageing
CGroup IV sulphides have larger $K_{s p}$ values than group II sulphides, so a higher $[S X^{2 -}]$ is needed
D $ZnS$ appears in group II because its ionic product exceeds $K_{s p}$ in dilute $HCl$

Answer: A, B, C

The ammoniacal medium shifts

H X_{2} S 2 H X^{+} + S X^{2 -}

to the right. In acid,

[S X^{2 -}]

is too low for ZnS, MnS, NiS and CoS, which is why they remain for group IV, so the last statement is false.

Practice Qualitative Analysis: Cations More on Group IV cations (Zn, Mn, Ni, Co)

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