Answer
(b) $[Co(NH3)_{5}NO_{2}]^{2+}$ is the correct answer.
Work Step by Step
Again simply by using set of IUPAC rules we can check which is the correct one here in the question the charge on cobalt is +3 so we can just do is simply check on which of these compound the charge on the cobalt is coming +3 and its done.
so here in option b) $[Co(NH3)_{5}NO_{2}]^{2+}$ that is coming +3 and so this is the correct answer.
if in some questions the charge comes same on more than 2 compounds we have to further check the rules bounded by which of the compounds is correct.
