Answer:
52.9 %.
Explanation:
Mg + 2HCl ---> MgCl2 + H2
Using the relative atomic masses of magnesium and hydrogen:
Theoretically 24.3 g of Mg will produce 2.016 g of H2
so 45.8 g will produce (2.016 * 45.8) / 24.3 = 3.80 g H2.
So the % yield = 2.01 * 100 / 3.80
= 52.9%.