‘25 volume’ hydrogen peroxide means  

25 volume H₂O₂  means:- 1 Lit of H₂O₂  on decomposition give 25 Lit of  O₂ at STP
$2{\mathrm{H}}_2{\mathrm{O}}_2\to 2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2$
$\mathrm{10\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}}\mathrm{volume}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}{\mathrm{H}}_2{\mathrm{O}}_2\to 30\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\mathrm{grams}/\mathrm{Lit}$
$\mathrm{25\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}}\mathrm{volume}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}{\mathrm{H}}_2{\mathrm{O}}_2\to \hspace{0.17em}\hspace{0.17em}\hspace{0.17em}?$
$\mathrm{=}\frac{25\times 30}{10}=75\hspace{0.17em}\hspace{0.17em}\hspace{0.17em}\mathrm{gms}/\mathrm{Lit}$