Question

In the complex $\left[Co(en{)}_{2}C{l}_2\right]Br$, the co-ordination number and oxidation state of cobalt are

• A. 6 and + 1
• B. 6 and + 3
• C. 3 and + 3
• D. 4 and + 2

Answer 1

Answer: (B)

Ethylene diamine (en) is a bidentate ligand, i.e., it has two donor centres. In the complex $\left[CO(en{)}_{2}C{l}_2\right]Br$, the total number of donor atoms is $6(4$ from two 'en' moles $+2C{l}^{-}$ions $)$.
Let the oxidation state of '$Co$' be $x$.
$x+(0\times 2)+(-1\times 2)+(-1)=0$
$x+0-2-1=0$
$x-3=0$
$x=+3$