If Ni$$^{2+}$$ is replaced by Pt$$^{2+}$$ in the complex [NiCl$$_2$$Br$$_2$$]$$^{2-}$$, which of the following properties are expected to get changed?
A. Geometry
B. Geometrical isomerism
C. Optical isomerism
D. Magnetic properties

Ni²⁺ (d⁸, 3d): With weak field ligands (Cl⁻, Br⁻), forms tetrahedral complex (paramagnetic, 2 unpaired electrons, no geometrical isomerism).

Pt²⁺ (d⁸, 5d): Always forms square planar complex (diamagnetic, 0 unpaired electrons, shows cis-trans isomerism).

Changes: A (geometry), B (geometrical isomerism now possible), D (magnetic properties). C (optical isomerism) does not change — neither tetrahedral [MX₂Y₂] nor square planar [MX₂Y₂] shows optical isomerism.

Answer: A, B and D.