Assertion (A): `pH` value of `HCN` solution decreases when `NaCN` is added to it.
Reason (R) : `NaCN` provides a common ion `CN^(Theta) to `HCN`.

Options

A. If both (A) and (R) are correc, and (R) is the correct explanation of (A).
B. If both (A) and (R) are correct but (R) is not the correct explanation of (A).
C. If (A) is correct, but (R) is incorrect.
D. If (A) is incorrect, but (R) is correct.

Answer

D

Explanation

`(A)` is wrong because addition of `NaCN` to `HCN`, due to common ion `(CN^(Theta))`. The degree of dissociation of `HCN` is supressed and hence less `[H^(o+)]` and increase in `pH. (R)` is correc.