Which of the following statements, with reference to a solution are correct?

(A) The osmotic pressure of the solution is proportional to the molarity of the solute.
(B) The elevation of the boiling point ($ΔT_b$) is directly proportional to the molal concentration of the solute in a solution.
(C) The unit of $K_b$ is $K\, kg^{-1}\, mol^{-1}$.
(D) $ΔT_b = T_b^0-T_b$

Choose the correct answer from the options given below:

(A) and (B) only

The correct answer is Option (2) → (A) and (B) only

Option 1: (A), (B) and (D) only

Statement (A) follows van’t Hoff’s equation $\pi = iMRT$, so osmotic pressure is proportional to molarity. (B) is also correct since $\Delta T_b = K_b m$, directly proportional to molality. However (D) is wrong because boiling point elevation is $T_b(\text{solution}) - T_b^\circ(\text{solvent})$, not the reverse.

Option 2: (A) and (B) only

Both (A) and (B) correctly state colligative property relations: osmotic pressure depends on molarity and boiling point elevation depends on molality. (C) has incorrect units and (D) has the wrong expression sign. So this set fits.

Option 3: (C) and (D) only

(C) is wrong because the correct unit of $K_b$ is $\text{K kg mol}^{-1}$, not $\text{K kg}^{-1} \text{mol}^{-1}$. (D) also reverses the definition of boiling point elevation. So both are incorrect.

Option 4: (B), (C) and (D) only

Although (B) is correct, (C) has incorrect units and (D) has the wrong formula sign. Hence the group is incorrect.