The density of a polyatomic gas in standard conditions is 0.795 kg m^-3. The specific heat of the gas at constant volume is : 

1400 J-kg^-1K^-1

Ideal gas equation for m grams of gas is : 

PV = mrT ... ( where r = specific gas constant)

\(\Rightarrow P = \frac{m}{V}rT = \rho r T\) 

r = \(\frac{P}{\rho T} = \frac{1.013*10^5}{0.795*273}\) = 466.7

Specific heat at constant volume ; 

\(c_v = \frac{r}{\gamma - 1}\)

\(c_v = \frac{466.7}{\frac{4}{3} - 1}\) = 1400 J/kg-K