Question 10.4:

Find the oxidation state of sodium in Na2O2.

Let the oxidation state of Na be x.
The oxidation state of oxygen, in case of peroxides, is –1.
Therefore,
$2\left(\mathrm{x}\right)+2\left(-1\right)=0\phantom{\rule{0ex}{0ex}}2\mathrm{x}-2=0\phantom{\rule{0ex}{0ex}}2\mathrm{x}=2\phantom{\rule{0ex}{0ex}}\mathrm{x}=+1$
Therefore, the oxidation sate of sodium is +1.