b
For polyatomi molecule has 3 translatioinal, 3 rotational degrees of freedom and \(f\) degrees of freedom for vibrational motion.

\(E=\frac{3 R T}{2}+\frac{3 R T}{2}+f R T\)

\(=3 R T+f R T\)

\(=(3+f) R T\)

\(C_{V}=\frac{d E}{d t}=(3+f) R\)

\(C_{P}=C_{V}+R=(3+f) R+R=(4+f) R\)

\(\gamma=\frac{C_{P}}{C_{V}}=\frac{4+f}{3+f}\)

\(\beta=\frac{4+f}{3+f}=\frac{4+2}{3+2}=1.2\)