\(a,n_{Mg}=\dfrac{7,2}{24}=0,3\left(mol\right)\\ PTHH:Mg+H_2SO_4\rightarrow MgSO_4+H_2\)
\(b,\) Theo PT: \(n_{H_2}=n_{Mg}=0,3\left(mol\right)\)
\(\Rightarrow V_{H_2\left(đktc\right)}=0,3\cdot22,4=6,72\left(l\right)\)
\(c,n_{H_2SO_4}=n_{Mg}=0,3\left(mol\right)\\ \Rightarrow C_{M_{H_2SO_4}}=\dfrac{0,3}{0,2}=1,5M\)