Chemistry Q54 – JEE-MAIN 2026

Which of the following statements are not correct ? A. For water, magnitude of

K_{b}

is more than the magnitude of

K_{f}

. B. The elevation in boiling point of water when a non-volatile solute is added to it is larger in magnitude than its depression in freezing point. C. Osmotic pressure measurement is preferred over any other colligative property to determine molar mass of proteins and polymers. D. The dimerised form of benzoic acid in benzene is

C_{6} H_{5} - C - O H \dots O = C - C_{6} H_{5}

. Choose the correct answer from the options given below :

Clue 1 of 3: Colligative Constants for Water

Recall the standard values for the ebullioscopic constant ( $K_{b}$ ) and cryoscopic constant ( $K_{f}$ ) for water.

🧠 Full Solution Path

Step 1: Evaluate Statements A and B (Colligative Properties of Water)✦ Active

For water, the ebullioscopic constant ( $K_{b}$ ) is approximately $0.512 {K kg mol}^{- 1}$ , and the cryoscopic constant ( $K_{f}$ ) is approximately $1.86 {K kg mol}^{- 1}$ . Thus, the magnitude of $K_{f}$ is greater than $K_{b}$ . Therefore, statement A, which claims $K_{b} > K_{f}$ , is **incorrect**.

The elevation in boiling point is $Δ T_{b} = K_{b} \cdot m$ , and the depression in freezing point is $Δ T_{f} = K_{f} \cdot m$ . Since $K_{f} > K_{b}$ for water, for the same molality ( $m$ ) of a non-volatile solute, $Δ T_{f}$ will be larger than $Δ T_{b}$ . Statement B claims $Δ T_{b}$ is larger than $Δ T_{f}$ , which is **incorrect**.

💡 Teacher's Secret Hint

Remember the specific values of $K_{b}$ and $K_{f}$ for water and their implications on the magnitude of $Δ T_{b}$ and $Δ T_{f}$ .

Step 2: Evaluate Statement C (Osmotic Pressure for Macromolecules)○ Expand

Osmotic pressure measurement is indeed preferred for determining the molar mass of proteins and polymers. This is because osmotic pressure is measured at room temperature, which prevents denaturation of biomolecules. Also, for macromolecules with high molar masses, the magnitude of osmotic pressure is significantly larger and more accurately measurable compared to the very small changes in freezing point depression or boiling point elevation.

Therefore, statement C is **correct**.

💡 Teacher's Secret Hint

Consider the practical advantages of osmotic pressure, especially for sensitive biological molecules and large molar masses.

Step 3: Evaluate Statement D (Dimerization of Benzoic Acid)○ Expand

Benzoic acid in non-polar solvents like benzene forms a cyclic dimer through two hydrogen bonds. The structure shown in statement D, $C_{6} H_{5} - C - O H \dots O = C - C_{6} H_{5}$ , depicts only one hydrogen bond and does not represent the cyclic dimer structure. The correct cyclic dimer involves two hydrogen bonds between the carboxyl groups of two benzoic acid molecules.

\begin{matrix} O....H-O \\ ||    | \\ C_{6} H_{5} - C C - C_{6} H_{5} \\ |    || \\ O-H....O \end{matrix}

Therefore, statement D is **incorrect**.

💡 Teacher's Secret Hint

Visualize the hydrogen bonding in the cyclic dimer of carboxylic acids. It involves two hydrogen bonds, not just one as ambiguously suggested by the given notation.

Step 4: Identify Incorrect Statements and Select Option○ Expand

Statements A, B, and D are incorrect. Statement C is correct. The question asks for the statements that are **not correct**.

Thus, the incorrect statements are A, B, and D. This corresponds to option 3.

💡 Teacher's Secret Hint

Carefully read the question to ensure you are identifying the 'not correct' statements, not the 'correct' ones.

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Chemistry Question 54 – JEE-MAIN 2026

Clue 1 of 3: Colligative Constants for Water

🧠 Full Solution Path