Assertion : The $\left[\mathrm{Ni}(\text { en })_3\right] \mathrm{Cl}_2$ (en = ethylene diamine) has lower…
Assertion : The $\left[\mathrm{Ni}(\text { en })_3\right] \mathrm{Cl}_2$ (en = ethylene diamine) has lower stability than $\left[\mathrm{Ni}\left(\mathrm{NH}_3\right)_6\right] \mathrm{Cl}_2$. Reason : In $\left[\mathrm{Ni}(\mathrm{en})_3\right] \mathrm{Cl}_2$ the geometry of $\mathrm{Ni}$ is trigonal bipyramidal.
If both assertion and reason are true and reason is the correct explanation of assertion
If both assertion and reason are true but reason is not the correct explanation of assertion
If assertion is true but reason is false
If both assertion and reason are false.
Solution
$\left[\mathrm{Ni}(\mathrm{en})_3\right] \mathrm{Cl}_2$ is a chelating compound and chelated complexes are more stable than similar complexes with unidentate ligands as dissociation of the complex involves breaking of two bonds rather than one. In $\left[\mathrm{Ni}(\mathrm{en})_3\right] \mathrm{Cl}_2, \mathrm{Ni}$ with $d^8$ configuration shows octahedral geometry. Six electrons will occupy the $t_{2 g}$ orbitals and two electrons will occupy the $e_g$ orbitals.