Why can dilute solutions of hydrogen peroxide not be concentrated by heating? How can a concentrated solution of hydrogen peroxide be obtained?

(N/A) $H_{2}O_{2}$ cannot be concentrated by heating because it decomposes much below its boiling point to give $H_{2}O$ and $O_{2}$.
$2H_{2}O_{2} \longrightarrow 2H_{2}O + O_{2}$
Therefore,concentration of $H_{2}O_{2}$ is carried out in a number of stages:
$(i)$ The $H_{2}O_{2}$ formed (about $1\%$) is extracted with water.
$(ii)$ The aqueous solution is concentrated by distillation under reduced pressure to give $30\% H_{2}O_{2}$ solution.