The ions from among the following which are colourless are:
(i) ${Ti}^{4 +}$ (ii) ${Cu}^{+}$ (iii) ${Co}^{3 +}$ (iv) ${Fe}^{2 +}$

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(iii) and (iv)

(ii) and (iii).

(i), (ii) and (iii)

(i) and (ii) only

answer is A.

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Detailed Solution

(i) Valence shell electron configuration of ${Ti}^{4 +} is 3 d^{0} 4 s^{0}$ . As there is no unpaired electrons for d-d transition, the solution of ions will be colourless.
(ii) Valence shell electron configuration of ${Cu}^{+} is 3 d^{10} 4 s^{0}$ . As all electrons are paired, there is no d-d transition, so the solution of ions will be colourless.
(iii) Valence shell electron configuration of ${Co}^{3 +} is 3 d^{6} 4 s^{0}$ . As there are 4 unpaired electrons, there is d-d transition of electron, so the solution of ions will be coloured.
(iv) Valence shell electron configuration of ${Fe}^{2 +} is 3 d^{6} 4 s^{0}$ . As there are 4 unpaired electrons, there is d-d transition of electron, so the solution of ions will be coloured.