(b)
$X(g) \rightarrow Y(g) + Z(g)$
The reaction is a first order reaction.
Hence ,
$k = \frac{0.693}{t_{1/2}} = \frac{2.303}{t}\log\frac{a}{(a - x)}$
$02234\ \frac{0.693}{10} = \frac{2.303}{t}\log\frac{a}{a/10}$
Or $t = \frac{2.303 \times 10}{0.693} \times \log 10$
=33min