In a binary electrolyte (AB type), the observed lowering of vapour pressure as compared to the theor — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

For a binary AB type electrolyte, maximum complete dissociation yields 2 ions. Thus, the van't Hoff factor $i = 1 + \alpha$. The observed colligative property is $i$ times the theoretical non-electrolyte value. Since the degree of dissociation $\alpha \le 1$, $i \le 2$. Due to interionic attractions in real finite solutions, $i$ is practically always strictly less than 2. Thus, the observed lowering can be greater than one and less than double, but it can never be *exactly equal* to double or *more* than double. Therefore, correct answer is A,B.