Match the following

	Complex		Colour
A)	$\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_4{{\mathrm{en}}^{\mathrm{aq}}}^{2+}\right.$	I)	Grey-green
B)	${\left[{\mathrm{Ni}}_1{\left({\mathrm{H}}_2\mathrm{O}\right)}_2{\left({\mathrm{en}}_2\right]}_{\mathrm{aq}}\right]}^{2+}$	II)	Violet
C)	${\left[\mathrm{Ni}(\mathrm{en}{)}_3\right]}_{\mathrm{aq}}^{2+}$	III)	Blue/Purple
D)	$\mathrm{Cr}\left[{\left({\mathrm{H}}_2\mathrm{O}\right)}_5\mathrm{Cl}\right]{\mathrm{Cl}}_2\cdot {\mathrm{H}}_2\mathrm{O}$	IV)	Pale blue

The correct match is
 

	A	B	C	D
1	IV	III	II	I
2	II	I	III	IV
3	I	IV	II	III
4	III	I	IV	II

$\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_4{{\mathrm{en}}^{\mathrm{aq}}}^{2+}\right.$-Pale blue

${\left[{\mathrm{Ni}}_1{\left({\mathrm{H}}_2\mathrm{O}\right)}_2{\left({\mathrm{en}}_2\right]}_{\mathrm{aq}}\right]}^{2+}$-Blue/Purple

${\left[\mathrm{Ni}(\mathrm{en}{)}_3\right]}_{\mathrm{aq}}^{2+}$-Violet

$\mathrm{Cr}\left[{\left({\mathrm{H}}_2\mathrm{O}\right)}_5\mathrm{Cl}\right]{\mathrm{Cl}}_2\cdot {\mathrm{H}}_2\mathrm{O}$ -Grey-green

Due to d-d transition  above all compounds shows colour , for strong field ligand CFSE increases and $\lambda$ value is decreases.