The correct option is C.
Justification:
Statement-1: This statement that vapour density remains constant during the course of reaction 2A(g) + 3B(g) → 4C(g) + D(g) is true. During a chemical reaction, the total number of moles of gases remains the same. Though the composition changes as reactants form products, the density does not change.
Statement-2: This statement that in all gaseous chemical reactions, vapour density remains constant is false. Not all gaseous reactions have constant vapour density. It depends on the number of moles of gases involved before and after the reaction. If the total number of moles remains the same, density will remain constant but not otherwise.
So, Statement-1 (about the given reaction) is true but Statement-2 (general statement) is false.
Hence, the correct option is C.
Statement-1 is True,
Statement-2 is False.
Does this help explain the justification? Let me know if any part is still not clear.