Let the oxidation state of $P t=x$, then
$(x \times 1)+3 \times(0)+(1 \times-1)+(1 \times-1)+(1 \times-1)=+1$
$x-3=+1$
$x=+4$
Thus, the $I U P A C$ name of the complex $\left[P t(N H)_{3} B r\left(N O_{2}\right) C l\right] C l$ is triamine bromidochloridonitro platinum $(IV)$ chloride as the names of the different ligands are arranged alphabetically.
$A: \left[ Ni ( en )_{3}\right]^{2+}, B :\left[ Ni \left( NH _{3}\right)_{6}\right]^{2+}, C :\left[ Ni \left( H _{2} O \right)_{6}\right]^{2+}$