Specific heat of an ideal gas for process $P{V}^x=$ constant is,

$C=\frac{R}{\gamma -1}-\frac{R}{x-1}$

$\mathit{C}=\mathit{R}\left\{\frac{1}{\frac{5}{3}-1}-\frac{1}{1.25-1}\right\}<0$

$\Rightarrow$ If heat is given to gas then temperature decreases and hence internal energy also decreases.

Also, $P{V}^{1.25}=$ constant

$PV=\frac{\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{t}}{V^{0.25}}$

$nRT=\frac{\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{n}\mathrm{t}}{V^{0.25}}$



$\Rightarrow$ Upon increase in pressure, volume decreases and Temperature increases.

If volume increases then temperature decreases and heat is absorbed by the gas.