I’m the reaction mg (s)+2hcl(aq), how many moles of hydrogen gas will be produced from 75.0 millimeters of a 1.0m hcl is an excess of mg?

75.0 ml = 0.0750 L of the solution of a 1.0M HCl
0.0750L*1.0 mol/L = 0.075 mol HCl in 0.0750 L of the solution of a 1.0M HCl

                                     Mg +2HCl > MgCl2 +H2
from reaction                       2 mol                          1 mol
                                              0.075 mol                    x mol

x=0.075*1/2 = 0.0375 mol H2