$n_{Al}=16,8/27≈0,6mol$
$a.2Al+3H_2SO_4\to Al_2(SO_4)_3+3H_2↑$
$\text{b.Theo pt :}$
$n_{H_2}=3/2.n_{Al}=3/2.0,6=0,9mol$
$⇒V_{H_2}=0,9.22,4=20,16l$
$\text{c.Theo pt :}$
$n_{Al_2(SO_4)_3}=1/2.n_{Al}=1/2.0,6=0,3mol$
$⇒m_{Al_2(SO_4)_3}=0,3.342=102,6g$
$m_{dd\ spu}=16,8+200-0,9.2=215g$
$⇒C\%_{Al_2(SO_4)_3}=\dfrac{102,6}{215}.100\%=47,72\%$