Match the following.

Complex Colour

I) $[Ni {(H_{2} O)}_{4} en {]_{aq}}^{2 +}$ A) Grey-green
II) ${[Ni {(H_{2} O)}_{2} {(en)}_{2}]}_{aq}^{2 +}$ B) Violet
III) $[Ni {(en)}_{3} {]_{aq}}^{2 +}$ C) Blue/Purple
IV) $[Cr {(H_{2} O)}_{5} Cl] {Cl}_{2} . H_{2} O$ D) Pale blue
Correct match is.

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D C B A

B A C D

A D B C

C A D B

answer is A.

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Detailed Solution

colour of the complex depends on the nature and charge of metal ion, strength of ligand.

$\begin{array}{l} \underset{green}{{[Ni {(H_{2} O)}_{6}]}^{+ 2}} (aq) + en (aq) ⇌ \underset{paleblue}{{[Ni {(H_{2} O)}_{4} (en)]}^{+ 2}} (aq) + 2 H_{2} O \\ \underset{}{{[Ni {(H_{2} O)}_{4} en]}^{+ 2}} (aq) + en (aq) ⇌ \underset{blue / purple}{{[Ni {(H_{2} O)}_{2} {(en)}_{2}]}^{+ 2}} (aq) + 2 H_{2} O \\ \underset{}{{[Ni {(H_{2} O)}_{2} {(en)}_{2}]}^{+ 2}} (aq) + en (aq) ⇌ \underset{violet}{{[Ni {(en)}_{3}]}^{+ 3}} (aq) + 2 H_{2} O \\ [Cr {(H_{2} O)}_{6}] {Cl}_{3} is violet; [Cr {(H_{2} O)}_{5} Cl] {Cl}_{2} . H_{2} O is grey - green \end{array}$