SSC JE Mechanical Engineering 2017 Set 1 Paper

As we already know that :
Cp – Cv = – T × ${\left(\frac{\mathrm{dS}}{\mathrm{dV}}\right)}_{\mathit{T}}\times {\left(\frac{\mathrm{dS}}{\mathrm{dP}}\right)}_{\mathit{T}}$
For Absolute Zero : A perfect crystal at Absolute Zero (0K) has Entropy (S) = 0 and according to the equation Cp - Cv tends to Zero, That's Why :
$\mathit{Y}=\left(\frac{\mathit{C}\mathit{p}}{\mathit{C}\mathit{v}}\right)=1$