Let's look at the reaction step by step. Aluminium carbide, typically represented as Al4C3, reacts with water to produce aluminium hydroxide and methane. The balanced reaction with H2O is: Al4C3+12H2O⟶4Al(OH)3+3CH4. When deuterium oxide ( D2O ) is used instead of water, every hydrogen atom is replaced by deuterium. Hence, aluminium hydroxide becomes aluminium deuteroxide, Al(OD)3, and methane becomes fully deuterated methane, CD4. The modified reaction becomes: Al4C3+12D2O⟶4Al(OD)3+3CD4. So, the product X′ in the reaction is CD4. Thus, the correct answer is Option D: CD4.