a
\((a)\)b \(\underset{\begin{smallmatrix}
s{{p}^{3}}{{d}^{2}}Hyb. \\
{{\mu }_{eff}}=2.8\,BM
\end{smallmatrix}}{\mathop{{{[Ni{{({{H}_{2}}O)}_{6}}]}^{2+}}+}}\,6N{{H}_{2}}\rightleftarrows \underset{\begin{smallmatrix}
s{{p}^{3}}{{d}^{2}}Hyb. \\
{{\mu }_{eff}}=2.8\,BM
\end{smallmatrix}}{\mathop{{{[Ni{{(N{{H}_{3}})}_{6}}]}^{2+}}}}\,+6{{H}_{2}}O\)