A mixture of $HCOOH$ and $H_2C_2O_4$ is heated with Conc.$H_2SO_4$.The gas produced is collected and on treating with KOH solution the volume of the gas decreases by $\large\frac{1}{6}$th.Calculate molar ratio of two acids in original mixture.

Question

$(a)\;2 : 1\qquad(b)\;4 : 1\qquad(c)\;3 : 2\qquad(d)\;1 : 2$