Answer:
0.50M (1 sig. fig.)
Explanation:
The problem objective is 'Molarity (M)', so set up given data to reduce to moles per liter. That is ...
Molarity = moles Mg/Liters of solution = (48.6g/24.31g·mole⁻¹)/(4Liters) = 0.499794323M (calc. ans.) ≅ 0.5M (1 sig. fig.)
