Question

Answer 1

\(m_{SO_4^{2-}}=38.8-10=28.8\left(g\right)\)

\(\Rightarrow n_{H_2SO_4}=n_{SO_4^{2-}}=\dfrac{28.8}{96}=0.3\left(mol\right)\)

\(n_{H_2}=0.3\left(mol\right)\)

\(V=0.3\cdot22.4=6.72\left(l\right)\)

Answer 2

$Mg + H_2SO_4 \to MgSO_4 + H_2$
$Cr + H_2SO_4 \to CrSO_4 + H_2$

Gọi $n_{H_2SO_4} = n_{H_2} = a(mol)$

Bảo toàn khối lượng : 

10 + 98a = 38,8 + 2a

=> a = 0,3

=> V = 0,3.22,4 = 6,72

Đáp án B