Relate the writing and balancing of a chemical equation to the principal of conservation of mass

Balancing a chemical reaction:

The reactants are written in terms of their chemical formula on the left hand side and the products are written in terms of their chemical formula on right hand side separated by an right arrow. The chemical symbols are followed by their physical states such as (l) for liquid, (s) for solid, (g) for gas and (aq) for aqueous.

The number of atoms on both sides of a  reaction must be equal in order to obey the law of conservation of mass.

Law of conservation of mass says the mass of reactants must be equal to the mass of products.

This is only possible when the reactants used are produced as products in the same quantities. Thus balancing of equation is done to follow the law of conservation of mass.

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-

the answer would be b i believe