Cp and Cv are specific heats at constant pressure and constant volume respectively. It is observed that Cp−Cv=a for hydrogen gas and Cp−Cv=b for nitrogen gas. The correct relation between a and b is:

For any gas, Cp−Cv=R, which is the gas constant. Hence be it any gas, hydrogen or nitrogen, its value is same. Here, for ideal gas, Cp−Cv=R/M, where M is the mass of one mole of gas. Mass of one mole of hydrogen M=2g and that of nitrogen M=28g
∴a=Cp−Cv=R/2 (for hydrogen)
And b=Cp−Cv=R/28 (for nitrogen)
⇒a=14b