Question

Three complexes,
$\left[CoCl\right(N{H}_3{)}_5{]}^{2+}\left(I\right)$,
$\left[Co\right(N{H}_3{)}_5{H}_{2}O{]}^{3+}\left(II\right)$ and
$\left[Co\right(N{H}_3{)}_6{]}^{3+}\left(III\right)$
absorb light in the visible region. The correct order of the wavelength of light absorbed by them is:

• A. $\left(III\right)>\left(I\right)>\left(II\right)$
• B. $\left(I\right)>\left(II\right)>\left(III\right)$
• C. $\left(II\right)>\left(I\right)>\left(III\right)$
• D. $\left(III\right)>\left(II\right)>\left(I\right)$

Answer 1

The correct option is B $\left(I\right)>\left(II\right)>\left(III\right)$

Solution:- (B) $\left(I\right)>\left(II\right)>\left(III\right)$

A complex having strong field ligand has the tendency to absorb light of the highest energy.

Among the three complexes, $\left[Co\right(N{H}_3{)}_6{]}^{3+}$ will absorb radiation of the highest energy and least wavelength.

$\left[Co\right(N{H}_3{)}_5{H}_{2}O{]}^{3+}$ has field weaker than the above compound and therefore absorbs radiation of lesser energy and more wavelength.

$\left]CoCl\right(N{H}_3{)}_5{]}^{2+}$ has the weakest field and therefore will absorb light of least energy and highest wavelength.

Strength of ligand: $N{H}_3>H_{2}O>C{l}^{-}$.