Aqueous solution of ${\mathrm{Ni}}^{2+}$ contains ${\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{2+}$ and its magnetic moment is 2.83 B.M. When ammonia is added in it, comment on the magnetic moment of solution:

Obtained reaction, 

${\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{2+}+6{\mathrm{NH}}_2\rightleftharpoons {\left[\mathrm{Ni}{\left({\mathrm{NH}}_3\right)}_6\right]}^{2+}+6{\mathrm{H}}_2\mathrm{O}$

since, ${\left[\mathrm{Ni}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right]}^{2+}$ and ${\left[\mathrm{Ni}{\left({\mathrm{NH}}_3\right)}_6\right]}^{2+}$ both have two unpaired electrons due to ${\mathrm{sp}}^3{\mathrm{d}}^2$ hybridization the value of B.M. is same.

Hence correct option is A.