Question

Assertion :A solution of $\left[Ni\right(H_{2}O{)}_6{]}^{2+}$ is green but a solution of $\left[Ni\right(C{N}_4){]}^{2-}$ is colourless. Reason: Energy difference between d levels $(i.e.\Delta )for{H}_{2}O$ complex (paramagnetic) is in the visible region and that for the cyano complex (diamagnetic) is in the UV region.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

Cyanide is stronger ligand than water. It causes much higher crystal field splitting. Energy difference between d levels (i.e.)for $\left[Ni\right(H_{2}O{)}_6{]}^{2+}$ complex (paramagnetic) is in the visible region and that for the $\left[Ni\right(C{N}_4){]}^2$ complex (diamagnetic) is in the UV region.
Hence $\left[Ni\right(H_{2}O{)}_6{]}^{2+}$ forms green color solution whereas $\left[Ni\right(C{N}_4){]}^2$ forms colorless solution.