The ratio $C_{p,m}/C_{V,m}$ for linear triatomic molecules including vibration contribution is given by

The ratio $C_{p,m}/C_{V,m}$ for linear triatomic molecules including vibration contribution is given by 1.154.

For a triatomic molecule 

$C_{V,\mathrm{m}}=\frac{3}{2}R+R+4R=\frac{13}{2}R;C_{p,\mathrm{m}}=\frac{13}{2}R+R=\frac{15}{2}R$

Hence, $C_{p,\mathrm{m}}/C_{V,\mathrm{m}}=15/13=1.154$

Hence, the option C is correct.