Call

1 mole of Mg reacts with 2 moles of HCl

24g of Mg reacts with 2 moles of HCl

1g of Mg will react with 2/24 moles of HCl

4g of Mg will react with 2/24 × 4 moles of HCl

= 0.33mole of HCl

Concentration of HCl = mole/volume

Volume = mole / concentration = 0.33/1.85 = 0.175L