$\underset{\begin{array}{l}1mole\\ \left(P\right)\end{array}}{{\left[Ni{\left(H_{2}O\right)}_6\right]}_{\left(aq\right)}^{2+}}\stackrel{+1moleen\left(aq\right)}{\to }Q\stackrel{+1moleen\left(aq\right)}{\to }R\stackrel{+1moleen\left(aq\right)}{\to }S$

When – en is Ethane –1,2 –diamine
Correct statement(s) about these complexes is/are
 

$P:{\underset{green}{\left[Ni{\left(H_{2}O\right)}_6\right]}}^{2+}$   $Q:{\underset{paleblue}{\left[Ni{\left(H_{2}O\right)}_4\left(en\right)\right]}}^{2+}$               $R:{\underset{blue/purple}{\left[Ni{\left(H_{2}O\right)}_2{\left(en\right)}_2\right]}}^{2+}$

$S:{\underset{violet}{\left[Ni{\left(en\right)}_3\right]}}^{2+}$

For the Octahedral complexes of Ni2+ only one electronic configuration possible. Hence, high spin and low spin complexes words not suitable.
D) ${\left[Ni{\left(en\right)}_3\right]}^{2+}$  geometrical isomerism not possible but optical isomerism possible.