Which chemical equation follows the law of conservation of mass?

The chemical equation presented in option A follows the law of conservation of mass.

The principle of conservation of mass states, mass can neither be created nor destroyed but can be transformed from one form to another.

A reaction that follows the law of conservation of mass,  must have equal number of moles each elements in reactants side and products side.

Only option A follows the law of conservation of mass;

Thus, we can conclude that the chemical equation presented in option A follows the law of conservation of mass.

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Option A

Explanation:

The expression that obeys the law of conservation of mass is choice A;

         2LiOH  +  H₂CO₃   →   Li₂CO₃  + 2H₂O

According to the law of conservation of mass; "in a chemical reaction, matter is neither created nor destroyed". By this law, mass is usually conserved.

The equation shows that mass is conserved because the number of moles of each specie is found on both sides

                                                Number of moles

                                 Li                   O                  H              C

Reactants                 2                    5                   4               1

Products                   2                    5                   4               1

This shows that mass is indeed conserved.