(a)
From the unit of rate constant ($i.e.,s^{- 1}),$ it is clear that the reaction is of first order.
$2N_{2}O_{5} \rightarrow 4NO_{2} + O_{2}$
Hence, for first order reaction ,
$k = \frac{2.303}{t}\log\frac{p_{0}}{p_{t}}$
$\therefore 3.38 \times 10^{- 5} = \frac{2.303}{10 \times 60}\log\frac{500}{p_{t}}$
Or $\log\frac{500}{p_{t}}$=0.00880
$\therefore\ \ \ \ \ \ \frac{500}{p_{t}} = anti\log{0.00880}$
=1.02
$p_{t} = \frac{500}{1.02} = 490\ atm$