Oxidation number of cobalt ion in [CoCl2(en)2]+ will be

The correct answer is Option (2) → 3

Let the oxidation number of Co be x. Chloride carries −1, ethane-1,2-diamine (en) is a neutral ligand, and the complex ion carries +1:

    \( x + 2(-1) + 2(0) = +1 \Rightarrow x = +3 \)

Cobalt is in the +3 state, as in \( \ce{[CoCl2(en)2]Cl} \), dichloridobis(ethane-1,2-diamine)cobalt(III) chloride.