Coordination number $6 \Rightarrow$ octahedral complex
$Ti$ is in $+4$ oxidations state $\Rightarrow$ no unpaired electrons
$\Rightarrow$ magnetic moment $= 0 \,B. M.$
$(I)\, [CrCl_2(NO_2)_2(NH_3)_2]^-$ $(II)\, [Co(NO_2)_3(NH_3)_3]$
$(III)\, [PtCl(NO_2)(NH_3 )(py)]$ $(IV)\, [PtBrCl(en)]$
$(I)\,\,\,-\,\,\,(II)\,\,\,-\,\,\,(III)\,\,\,-\,\,\,(IV)$