Which of the following is a correct statement?

Which of the following is a correct statement?
  1. Aqueous solutions of $\mathrm{Cu}^{+}$and $\mathrm{Zn}^{2+}$ are colourless
  2. Aqueous solutions of $\mathrm{Cu}^{2+}$ and $\mathrm{Zn}^{2+}$ are colourless
  3. Aqueous solution of $\mathrm{Fe}^{3+}$ is green in colour
  4. Aqueous solution of $\mathrm{MnO}_4^{-}$is colourless

Solution

(a) $\mathrm{Cu}^{+}=[\mathrm{Ar}] 3 d^{10}$
(No unpaired electrons, so it is colourless) $\mathrm{Zn}^{2+}=[\mathrm{Ar}] 3 d^{10}$ (No unpaired electrons, so it is colourless) (b) $\mathrm{Cu}^{2+}=[\mathrm{Ar}] 3 d^9$
(One unpaired electron is present, so it is coloured) $\mathrm{Zn}^{2+}$ is colourless. (c) The colour of $\mathrm{Fe}^{2+}$ is green while that of $\mathrm{Fe}^{3+}$ is blue. (d) $\mathrm{MnO}_4^{-}$contains no unpaired electrons, however, it is coloured due to charge transfer. Thus, only statement given in option (a) is correct.

Asked in: AP EAMCET 2010

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