Final answer:
Two water molecules can be chemically decomposed into two oxygen and two hydrogen molecules without violating the conservation of mass, through a reaction that requires energy.
Step-by-step explanation:
Two water molecules (H2O) can indeed be used to make two molecules of oxygen (O2) and two molecules of hydrogen (H2) through a chemical reaction. This process involves breaking the chemical bonds in the water molecules and reforming new bonds to create diatomic oxygen and hydrogen molecules. The reaction requires an input of energy to overcome the activation barrier and can be represented by the reverse of the balanced chemical equation: 2 H2O → 2 H2 + O2. Therefore, the correct answer is: (a) Yes, through chemical reactions. This does not violate the conservation of mass as the number of atoms remains the same before and after the reaction, hence answer (b) is incorrect. While energy is indeed required for this endothermic reaction, the critical factor is the reaction itself (answer c), and although temperature and pressure do affect reaction rates, they do not determine the possibility of the reaction (answer d).