Properties of gases

Determine the molecular mass $M,$ specific gas constant $R,$ mass$-$specific energy $e$ for a gas at $500$ Kelvin that consists purely of$,$

$($a$)$ Carbon dioxide

$($b$)$ Methane

$($c$)$ Krypton

You may assume that the vibrational modes are inactive, but explicitly show where this assumption enters into your calculations.