a,
Thăng bằng e:
$1\times| \mathop{Al}\limits^0\to \mathop{Al}\limits^{+3}+3e$
$1\times| \mathop{N}\limits^{+5}+3e\to \mathop{N}\limits^{+2}$
$\Rightarrow Al+4HNO_3\to Al(NO_3)_3+NO+2H_2O$
b,
$n_{Al}=\dfrac{2,7}{27}=0,1(mol)$
$\Rightarrow n_{NO}=n_{Al}=0,1(mol)$
$\to V=0,1.22,4=2,24l$