(a) Balanced chemical equation has an equal number of atoms of different elements in the reactants and products. According to law of conservation of mass, matter can neither be created nor be destroyed in a chemical reaction.
(b)(i) P4 (s) + 10Cl2 (g) ———> 4PCl5 (S)
(i)CH4 (g) + 2O2 (g) ———> CO2 (g) + 2H2O(l) + heat energy
(iii) C6H12O6 (s) + 6O2 (g) + 6H2O ———> 6CO2 (aq) + 12H2O (l) + energy