Which of the following statements are not…

Single correct+4 / -1Answer matches NTA’s final key

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 drawn as C $_6$ H $_5$ –C(=O)–OH ···· O=C(OH)–C $_6$ H $_5$ .

Choose the correct answer from the options given below:

Solution

A, not correct. For water $K_b = 0.52$ K kg mol⁻¹ and $K_f = 1.86$ K kg mol⁻¹, so $K_f$ is larger.
B, not correct. For the same molality $\Delta T = K \cdot m$ , so the freezing-point depression is the larger change.
C, correct. Osmotic pressure is measured at room temperature and gives a sizeable reading even for the tiny molar concentrations of large molecules, so it is the method of choice for proteins and polymers.
D, not correct. The benzoic acid dimer is a cyclic structure held by two hydrogen bonds, each O–H of one molecule bonding to the C=O of the other. The structure shown has only one.

The incorrect statements are A, B and D.

Answer: A, B and D only.

Answer checked against the official answer key. The solution is our own working.