After 5 minutes, 1.98 × 10-3 moles of hydrogen gas is produced. how many grams of magnesium reacted?

0.048 g

We are given;

We are required to calculate the mass of Magnesium that reacted

Mg + 2HCl → MgCl₂ + H₂

1 mole of magnesium reacts with 2 moles of HCl to produce 1 mole of MgCl₂ and 1 mole of hydrogen gas

Mole ratio of Mg : H₂ is 1 : 1

Thus, moles of Mg = Moles of H₂

Moles of Mg is 1.98 × 10^-3 moles

But, molar mass of Mg = 24.305 g/mol

Therefore;

Mass of Mg = 1.98 × 10^-3 moles × 24.305 g/mol

                  = 0.048 g

The mass of Mg that reacted is 0.048 g

it is b that is the answer.