The Vapour density of a compound is 39. It contains carbon and hydrogen atoms in the ratio $1:1$. Its molecular formula is

Molecular mass of Compound = vapour density $\times 2$ $=39\times 2=78$

Let the number of carbon and Hydrogen atoms be " $x$ ".

then, 78=12(x)+1(x)=13 x

x = 6

$So$, the molecular formula is $C_6{H}_6$. 

Hence, option (C) is correct.