In the reaction mg(s)+2hcl(aq)→mgcl2(aq)+h2(g) + mgcl2 (aq) how many grams of hydrogen gas will be produced from 125.0 milliliters of a 6.0 m hci in an excess of mg

The reaction 
Mg(s) + 2HCl(aq) = MgCl2(aq) + H2(g) +MgCl2 
Moles of HCl used will be;
 = 0.125 l × 6.0 M
 = 0.75 moles 
The mole ratio of HCl to H2 is 2:1
Therefore; moles of Hydrogen is 0.75/2 = 0.375 mole
Molecular mass of hydrogen is 2 g
Hence; the mass of hydrogen = 2 × 0.375 = 0.75 g

Alpha particles have positive charge, beta particles have negative charge, and answer 4 just doesn’t make sense. thus, you are left with only one possible answer.