While there is no such thing as 100 percent safe, having nuclear energy is much safer than you think. It's thousands of times safer than conventional coal and other fossil-fuel-derived energy, not to mention the specter of environmental disaster from continued use of carbon-based energy sources.
Chemical Reactions and Moles of Reactants and Products
That is, it requires 2 moles of magnesium and 1 mole of oxygen to produce 2 moles of magnesium oxide. If only 1 mole of magnesium was present, it would require 1 ÷ 2 = ½ mole of oxygen gas to produce 2 ÷ 2 = 1 mole magnesium oxide.