Initial temperature = 300 K
Let no. of mole at 300K = n
Let new temperature be = T K
Mole coming out at T K = $\large\frac{1}{3} n$
Mole left at T K =$ n - \large\frac{1}{3}n$
$ \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\; = \large\frac{2}{3}n$
Under constant P and V
$n_1T_1 = n_2T_2$
$n\times300 = \large\frac{2}{3}n\times T$
T = 450 K
$ = 177^{\large\circ}C$
Hence answer is (A)