Question

Oxidation number of P in ${KH}_2{PO}_3$ is:

• A. $-1$
• B. $-3$
• C. $+5$
• D. $+3$

Answer 1

Answer: (D)

$+3$

Molecular formula $=K{H}_{2}P{O}_3$

Overall charge on compound $=0$

Oxidation no. of oxygen in compound $=-2$

Oxidation no. of hydrogen in compound $=+1$

Oxidation no. of potassium in compound $=+1$

Let the oxidation no. of phosphorous be x.

Sum of oxidation no. of atoms = overall charge on atom

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

$\Rightarrow 1+2+x-6=0$

$\Rightarrow x-3=0$

$\Rightarrow x=+3$

Hence, the oxidation number of P is +3.