$PTHH :$
$2Zn+O_2\overset{t^o}\to 2ZnO$
$a.n_{ZnO}=40,5/81=0,5mol$
$\text{Theo pt :}$
$n_{O_2}=1/2.n_{ZnO}=1/2.0,5=0,25mol$
$⇒V_{O_2}=0,25.22,4=5,6l$
$b.2KClO_3\overset{t^o}\to 2KCl+3O_2$
$\text{Theo pt :}$
$n_{KClO_3}=2/3.n_{O_2}=2/3.0,25=\dfrac{1}{6}mol$$
$⇒m_{KClO_3}=\dfrac{1}{6}.122,5=\dfrac{245}{12}g$