Conservation of mass (mass is never lost or gained in chemical reactions), during chemical reaction no particles are created or destroyed, the atoms are rearranged from the reactants to the products.
The law of conservation of energy states that the total energy of an isolated system remains constant; energy can neither be created nor destroyed; it can only be transformed or transferred from one form to another.
C and D are not correctly balanced so it is not show conservation of energy also for B the energy value is not correct it is not show conservation of mass and energy so the correct answer is A: 2 H₂(g) + O₂(g) → 2 H₂O(g) +483.6 kJ