Answer: 6.1 g
Explanation:
between Mg and MgO theres a 1;1 MOLE RATIO
here's the balanced equation
2Mg + O2 ==> 2MgO
24g of magnesium is approximately 1 mole of magnesium so it produces 40 g of mgo which is also 1 mole of mgo thus 10/40 =0.25 moles of MgO so 0.25 moles of magnesium would be needed which is approximately 6.1 g