Answer : 1. "2Mg + O2 ----> 2MgO"
Explanation :

Answer: A) 2Mg + O2 ----> 2MgO Explanation: Given Equation is  Mg + O2 → MgO Balancing the Chemical Equation is nothing but Conservation of Matter. As Matter is Neither created nor Destroyed, it must be conserved. Here we have 1 Mg and 2 O on the left side and 1 Mg and 1 O on the right side To balance that, add 1 Mg on the left side so that it becomes 2 Mg and 2 O on the left side i.e, 2 Mg + O2 → 2 MgO Here it has 2 Mg & 2 O on the left side and 2 Mg and 2 O on the right side and the Chemical equation is Balanced.