(b) The given relation is $p \propto V$
Therefore, $p \propto V$
When $V$ chnages from $V$ to $2V$, pressure $p$ is also doubled
For an ideal gas, $\frac{pV}{T} =$constant
$\therefore\ T \propto pv$. Hence, $T$ becomes $2 \times 2 = 4$ times
$ie,\ 4 \times 300\ K = 1200\ K$