The correct option is B C+O2→CO2
Law of conservation of mass states that mass can neither be created nor destroyed. Matter can change forms but the mass remains conserved.
Hence, in a chemical reaction, mass of the products is equal to the mass of the reactants. This is only possible if the chemical equation is correctly balanced i.e., number of atoms of each element is same on both the sides of the equation.
The only reaction which is balanced is:
C(s)+O2(g)→CO2(g)