Which of the following transition metal ions is not coloured?

Question

Which of the following transition metal ions is not coloured? (A)  Cu+  (B)  V3+  (C)  Co2+  (D)  Ni2+

Tardigrade Admin · Accepted Answer

Presence of unpaired electron is a necessity for transition metal ions to give colour.
The electronic configuration of given transition metal ions are as

_{29} C u^{+} = [A r] 3 d^{10} 4 s^{0}

(no unpaired electron)

_{23} V^{3 +} = [A r] 3 d^{2} 4 s^{0}

(two unpaired electrons)

_{27} C o^{2 +} = [A r] 3 d^{7} 4 s^{0}

(three unpaired electrons)

_{28} N i^{2 +} = [A r] 3 d^{8} 4 s^{0}

(two unpaired electrons)
Thus,

C u^{+}

ion is colourless.

Q. Which of the following transition metal ions is not coloured?

$C u^{+}$

$V^{3 +}$

$C o^{2 +}$

$N i^{2 +}$