Answer:
0.81 moles H2
Explanation:
The equation of the reaction is;
Mg(s) + 2HCl(aq) ------>MgCl2(aq) + H2(g)
Number of moles of HCl reacted = concentration * volume
Number of moles of HCl reacted = 6.44 * 250/1000
Number of moles of HCl reacted = 1.61 moles of HCl
If 2 moles of HCl produces 1 mole of H2
1.61 moles of HCl produces 1.61 * 1/2 = 0.81 moles H2