Which among the following will be named as dibromidobis(ethylenediamine)chromium(III) bromide?

The ligands attached to ${\mathrm{Cr}}^{3+}$ species within the coordination sphere are two Br- ions and two neutral ethylenediamine. The remaining one positive charge requires the presence of one  ion outside the coordination sphere. This requirement is satisfied by the choice (b ).

(a) We first name cation and then anion.

(b) If cation is complex, then we first name ligand in alphabetical order and then central atom with oxidation state remain numeral in common brackets.

[Cr(en)2​Br2​]Br − is named as dibromidobis (ethylenediamine) chromium(III) bromide :

Ligands are : Br (two), ethyenediammine (two).

Central ion : Cr(III) or Cr3+

Counter ion : Br−