Which best describes how to balance the chemical equation shown below to support the law of conservation of mass? Mg + O2 → MgO

2 Mg(s) + O2(g) → 2 MgO(s)

Explanation:

As magnesium (Mg) has a valency of +2, and oxygen (O) has a valency of -2, the ratio would be 1:1, and magnesium oxide would be represented as MgO. The number of atoms of each element on reactant and product side must be equal. That is the basic principle for balancing an equation.

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i just got this problem. it's 90.3

i believe the answer is a.