S-1: The `[Co(o x)_(3)]^(3-)` complex is diamagnetic andgains stability through chelation.
S-2: The `[Co(NO_(2))_(6)]^(4)` is inner orbital complex involving `d^(2)sp^(3)` hybridisation and is paramagnetic.
S-3: The complex `[PtCl_(4)]^(2-)` is square planar and is diamagnetic.

Options

A. T T T
B. F F T
C. T F T
D. T T F

Explanation

(A), `S_(1):(o bx)` is chelating ligand and thus provides extra stability through chelation `["Co(ox)"_(3)]^(3-)`

It is dimagnetic and has `d^(2)sp^(3)` hydrolisation. `S_(2): NO_(2)^(-)` is a stronger ligand and with `d^(7)` configuration to give `d^(2)sp^(3)` hybridisation one of the 3d-electron jumps to higher energy orbital giving the complex paramagnetic character. `S_(3)`: Pt(II) has `5d^(8)` configureation which has greater CFSE `[PtCl_(4)]^(2-)`

Hence, complex is square planar and diamagnetic