Question

The oxidation state of oxygen in $$H_2{O}_2$$ is :
A . $+1$
B . $-1$
C . $+2$
D . $-2$

Answer 1

Hint : We know that the oxidation number can be defined as the total number of electrons that an atom donates or accepts in order to form a chemical bond with another atom. When the oxidation state of any atom changes during the reaction it means that it is giving information about the transfer of electrons.An element can have multiple oxidation states.

Complete step by step answer:
Hydrogen atoms usually have $+1$ oxidation number except in metal hydrides where it is $-1$ and oxidation number of oxygen atoms is usually $-2$ but it is not the same in all the molecules. In hydrogen peroxide ,the oxidation number of hydrogen is $+1$ but its oxidation number is $-1$ when hydrogen is combined with less electronegative elements. Since here in hydrogen peroxide oxygen atom is more electronegative than hydrogen therefore oxidation number of hydrogen atom will be $+1$ .Now we will calculate oxidation number of oxygen in hydrogen peroxide.
Let the oxidation number of oxygen atoms in hydrogen peroxide be x. We know that the sum of the oxidation numbers of all atoms in neutral compound is zero .We can calculate oxidation number of oxygen atom in $$H_2{O}_2$$ by taking the sum of the oxidation number of all atoms of $$H_2{O}_2$$.
$\begin{array}{c}\Rightarrow (x\times 2)+((+1)\times 2)=0\\ \Rightarrow 2x+2=0\\ \Rightarrow x=-1\end{array}$
So the oxidation state or oxidation number of oxygen in hydrogen peroxide ($$H_2{O}_2$$) is $-1$.

Hence in the given question option B is the correct answer that is $-1$ .

Note: We have approached this problem with the concept that the oxidation state of hydrogen peroxide is zero and we know the oxidation number of hydrogen atom that is $+1$ . Then it becomes very easy to calculate the oxidation number of oxygen in the molecule by assuming the oxidation number of oxygen as x. Hence we have calculated the oxidation number of oxygen in hydrogen peroxide is $-1$ .