The volume of oxygen required for the complete burning of 100 ml of acetylene at STP is

${\mathrm{C}}_2{\mathrm{H}}_2+\frac{5}{2}{\mathrm{O}}_2\to 2{\mathrm{CO}}_2+{\mathrm{H}}_2\mathrm{O}$

$1 \mathrm{mole} \to \frac{5}{2} \mathrm{mole} {\mathrm{O}}_2$

$22.4 \mathrm{lit} \to \frac{5}{2}\times 22.4 \mathrm{lit}$

$\mathrm{o}.1\to ?$

$=\frac{0.1}{22.4}\times \frac{5}{2}\times 22.4$

=0.25lit $\times$1000 

= 250 ml