(a)
$TV^{\gamma - 1} =$constant
$\frac{T}{T_{final}} = \left( \frac{V_{2}}{V_{1}} \right)^{\gamma - 1}$
$\frac{T}{T_{final}} = \left( \frac{2}{1} \right)^{(\frac{5}{3} - 1)} = 2^{\frac{(2}{3})}$
$\frac{T}{T_{final}} = \frac{T}{2^{\frac{(2}{3})}}$