If $\mathrm{Ni}^{2+}$ is replaced by $\mathrm{Pt}^{2+}$ in the complex $\left[\mathrm{NiCl}_{2} \mathrm{Br}_{2}\right]^{2-}$, which of the following properties are expected to get changed ?

A. Geometry

B. Geometrical isomerism

C. Optical isomerism

D. Magnetic properties