Question

In which of the following coordination compounds do the transition metals have an oxidation number of $+6$?

• A. $\left[Cr\right(H_{2}O{)}_{4}C{l}_2]Cl\cdot 2H_{2}O$
• B. $\left[Fe\right(CO{)}_5]$
• C. $\left[\right(H_{2}O{)}_{5}Cr-O-Cr(H_{2}O{)}_5{]}^{4+}$
• D. $K_2\left[Cr\right(CN{)}_2{O}_2\left(O_2\right)N{H}_3]$

Answer 1

Answer: (D)

$K_2\left[Cr\right(CN{)}_2{O}_2\left(O_2\right)N{H}_3]$

1. $\left[Cr{\left(H_{2}O\right)}_4{Cl}_2\right]Cl.2H_{2}O$

Let oxidation state of $Cr$ $=x$

Oxidation state of $Cl$ $=-1$

Oxidation state of $H_{2}O$ $=0$

$x+4\left(0\right)+2(-1)+(-1)+2\left(0\right)=0$

$x=+3$

2. $\left[Fe{\left(CO\right)}_5\right]$

Let oxidation state of $Fe$ $=x$

Oxidation state of $CO$ $=0$

$x+5\left(0\right)=0$

$x=0$

3.${[{\left(H_{2}O\right)}_{5}Cr-O-Cr{\left(H_{2}O\right)}_5]}^{4+}$

Let oxidation state of $Cr$ $=x$

Oxidation state of $H_{2}O$ $=0$

Oxidation state of $O$ $=-2$

Total charge on compound $=+4$

$5\left(0\right)+x+(-2)+x+5\left(0\right)=+4$

$2\left(x\right)=6$

$x=+3$

4.$K_2\left[Cr(CN{)}_2{O}_2\right(O_2\left)N{H}_3\right]$

Let oxidation state of $Cr$$=x$

Oxidation state of $N{H}_3$$=0$

Oxidation state of $O$$=-2$

Oxidation state of $O_2$$=-2$$ as it is peroxido lignad.

Oxidation state of $CN$$=-1$

Oxidation state of $K$$=+1$

$2(+1)+x+2(-1)+2(-2)+(-1)+\left(0\right)=0$

$x=+6$

So (D) is correct answer.