Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) From the equation above, the mass of magnesium required to react with 250cm3 of 0.5M HCl is [Mg = 24]

The given equation shows a reaction between magnesium and hydrochloric acid which produces magnesium chloride and hydrogen gas. The question asks for the mass of magnesium required to react with a given amount of hydrochloric acid. To solve this problem, we need to use the following formula: moles = concentration x volume / 1000 where moles is the number of moles of hydrochloric acid, concentration is the molarity of hydrochloric acid, and volume is the volume of hydrochloric acid in liters. First, we need to calculate the number of moles of hydrochloric acid in 250 cm³ of 0.5 M HCl: moles HCl = 0.5 x 250 / 1000 = 0.125 moles From the balanced chemical equation, we know that 1 mole of magnesium reacts with 2 moles of hydrochloric acid to produce 1 mole of hydrogen gas. Therefore, the number of moles of magnesium required is half the number of moles of hydrochloric acid: moles Mg = 0.125 / 2 = 0.0625 moles Finally, we can calculate the mass of magnesium required using its molar mass: mass = moles x molar mass = 0.0625 x 24 = 1.5 g Therefore, the answer is option B: 1.5g.