Final answer:
Among the given options, the balanced chemical equation is C. 2Ca(s) + O2(g) ⇒ 2CaO(s), as it conserves the number of atoms for each element on both sides of the equation.
Step-by-step explanation:
The balanced chemical equation among the options is C. 2Ca(s) + O2(g) ⇒ 2CaO(s). For an equation to be balanced, it must have the same number of each type of atom on both sides of the reaction. In 2Ca(s) + O2(g) ⇒ 2CaO(s), there are 2 calcium atoms and 2 oxygen atoms on both sides of the equation, which satisfies the law of conservation of mass.
For example, choice A, 3Ca(s) + O2 ⇒ CaO(s), is unbalanced because it has 3 calcium atoms on the left but only 1 calcium atom on the right. Similarly, choice B, Ca(s) + O2(g) ⇒ 2Ca(s), is incorrect as the product has more calcium atoms than the reactants. Choice D, 6Ca(s) + O2(g) ⇒ 2CaO(s), is also unbalanced due to having more calcium atoms on the reactant side than the product side.