5 ml of unsaturated hydrocarbon requires 15 ml of Oxygen for complete combustion to produce 10 ml of carbondioxide. Formula of Hydrocarbon is

$C_x{H}_y+\left(x+\frac{y}{4}\right)O_2\to xC{O}_2+\frac{y}{2}{H}_{2}O$

$5ml$     $\hspace{0.17em}\hspace{0.17em}5\left(x+\frac{y}{4}\right)$                5X               $\frac{5y}{2}$

Given 5x = 10

                x = 2

$5\left(x+\frac{y}{4}\right)=15$

$x+\frac{y}{4}=3$

$\frac{y}{4}=1$

Y = 4

Formulae =${\mathrm{C}}_2{\mathrm{H}}_4$