$\left[ Co ( ox )_{2} Br \left( NH _{3}\right)\right]^{2 -}$ i.e. $\simeq\left[ M ( AA )_{2} ab \right]^{2-}$
$\rightarrow$ cis is optically active isomers and trans is optically inactive isomer
$\rightarrow$ Hence total isomers is $=3$
$(1) $ $[Ag(NH_3)_2]^{+}$ - રેખીય
$ (2) $ $[MnCl^4]^{2-}$ - ચતુષ્ફલકીય
$(3) $ $[Cu(NH_3)_4]^{2+}$ - ચોરસ સમતલ
$(4) $ $[Ni(CN)_4]^{2-}$ - ચોરસ સમતલ