Q93 / 180 · AIIMS 2002 · Chemistry

Assertion : Cuprous ion $\left(\mathrm{Cu}^{+}\right)$is colourless whereas cupric ion $\left(\mathrm{Cu}^{++}\right)$is blue in the aqueous solution. Reason : Cuprous ion $\left(\mathrm{Cu}^{+}\right.$) has unpaired electrons while cupric ion $\left(\mathrm{Cu}^{++}\right.$) does not.

  • A
    If both the assertion and reason are true and reason is a correct explanation of the assertion.
  • B
    If both assertion and reason are true but assertion is not a correct explanation of the assertion.
  • Correct answer
    C
    If the assertion is true but the reason is false.
  • D
    If both assertion and reason are false.

Solution

Cuprous ions $\left(\mathrm{Cu}^{+}\right)$is colourless because it has no unpaired electrons in the $3 d$ sub-shell as it has $3 d^{10}$ configuration. The cupric ion $\left(\mathrm{Cu}^{++}\right)$has one unpaired electron as it has configuration $3 d^9$. By absorbing the visible light, the unpaired electron can migrate from one set of $d$-orbitals to another under the applied field of water molecules. Hence, cupric ion $\left(\mathrm{Cu}^{++}\right)$in aqueous solution shows blue colour.

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

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