Q20 / 120 · VITEEE 2011 · Chemistry

Assertion (A) $\mathrm{Cu}^{2+}$ and $\mathrm{Cd}^{2+}$ are separated by first adding $\mathrm{KCN}$ solution and then passing $\mathrm{H}_{2} \mathrm{~S}$ gas. Reason (R) $\mathrm{KCN}$ reduces $\mathrm{Cu}^{2+}$ to $\mathrm{Cu}^{+}$and forms a complex with it. The correct answer is

  • A
    Both (A) and (R) are true and (R) is the correct explanation of (A)
  • Correct answer
    B
    Both (A) and (R) are true but (R) is not the correct explanation of (A)
  • C
    (A) is true but (R) is not true
  • D
    (A) is not true but (R) is true

Solution

$\mathrm{KCN}$ forms complex with $\mathrm{Cu}^{+}$and $\mathrm{Cd}^{2+}$ as $\mathrm{K}_{3}\left[\mathrm{Cu}(\mathrm{CN})_{4}\right]$ and $\mathrm{K}_{2}\left[\mathrm{Cd}(\mathrm{CN})_{4}\right]$ respectively. On passing $\mathrm{H}_{2} \mathrm{~S}$, only $\mathrm{Cd}^{2+}$ complex gets decomposed to yellow CDS.

Hence, the correct answer is option: 'B'.

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