Question

The oxidation state and coordination number of cobalt in the complex $CoC{l}_3.5N{H}_3$ are respectively:

• A. 3 and 6
• B. 6 and 3
• C. 6 and 2
• D. 5 and 3

Answer 1

The correct option is A 3 and 6

Oxidation state of $Co$ is $+3$ (i.e., $x-3=0,x=+3$).

The complex can be represented as $\left[Co\right(N{H}_3{)}_{5}Cl]C{l}_2$, which on ionization gives $\left[Co\right(N{H}_3{)}_{5}Cl{]}^{2+}$ and two $C{l}^{-}$.

Here, five $N{H}_3$ and one $Cl$ form co-ordinate bonds to $C{o}^{3+}$, forming a complex ion. Hence, coordination number is 6.