Perhydrol means $30 \%$ solution of $H _{2} O _{2}$.
$ H _{2} O _{2}$ decomposes as
$2 H _{2} O _{2} \rightarrow 2 H _{2} O + O _{2}$
Volume strength of $30 \% H _{2} O _{2}$ solution is $100$ that means $1 \,mL$ of this solution on decomposition gives $100 \,mL$ oxygen.
Since, $100 \,mL$ of oxygen is obtained by $=1\, mL$ of $H _{2} O _{2}$
$\therefore 1000\, mL$ of oxygen will be obtained by
$=\frac{1}{100} \times 1000\, mL $ of $H _{2} O _{2} $
$=10 \,mL$ of $H _{2} O _{2}$
