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Solutions · Question 21

JEE Main 2026 (Online) 21st January Morning ShiftMCQEasy📈 Topic in 13% papers+4−1
1

Elements P and Q form two types of non-volatile, non-ionizable compounds PQ and PQ2. When 1 g of PQ is dissolved in 50 g of solvent 'A', Tb was 1.176 K while when 1 g of PQ2 is dissolved in 50 g of solvent 'A', Tb was 0.689 K. (Kb of 'A' = 5 K kg mol-1). The molar masses of elements P and Q (in g mol-1) respectively, are :

  1. 25, 60
  2. 60, 25
  3. 65, 145
  4. 70, 110

Answer

(1) 25, 60

Solution

Tb = Kb wB 1000MB wA

MB = Kb wB 1000 Tb wA

For PQ: MPQ = 5 1 10001.176 50 = 500058.8 = 85 g mol-1

For PQ2: MPQ2 = 5 1 10000.689 50 = 500034.45 = 145 g mol-1

P + Q = 85 and P + 2Q = 145

Q = 145 − 85 = 60 g mol-1

P = 85 − 60 = 25 g mol-1

Answer: (1)

JEE Main 2026 (Online) 21st January Morning Shift

Keep practising — Solutions

2

The osmotic pressure of a living cell is 12 atm at 300 K. The strength of sodium chloride solution that is isotonic with the living cell at this temperature is g L-1. (Nearest integer) Given : R = 0.08 L atm K-1 mol-1 Assume complete dissociation of NaCl (Given: Molar mass of Na and Cl are 23 and 35.5 g mol-1 respectively.)

JEE Main 2026 (Online) 21st January Evening Shift
3

A substance 'X' (1.5 g) dissolved in 150 g of a solvent 'Y' (molar mass = 300 g mol-1) led to an elevation of the boiling point by 0.5 K. The relative lowering in the vapour pressure of the solvent 'Y' is 10-2. (nearest integer) [Given: Kb of the solvent = 5.0 K kg mol-1] Assume the solution to be dilute and no association or dissociation of X takes place in solution.

JEE Main 2026 (Online) 21st January Evening Shift
4

HA(aq) H+(aq) + A-(aq) The freezing point depression of a 0.1 m aqueous solution of a monobasic weak acid HA is 0.20 C. The dissociation constant for the acid is Given: Kf(H2O) = 1.8 K kg mol-1, molality ≡ molarity

  1. 1.90 10-3
  2. 1.38 10-3
  3. 1.1 10-2
  4. 1.89 10-1
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5

Which of the following binary mixtures does not show the behaviour of minimum boiling azeotropes?

  1. CH3OH + CHCl3
  2. C6H5OH + C6H5NH2
  3. H2O + CH3COC2H5
  4. CS2 + CH3COCH3
JEE Main 2025 (Online) 8th April Evening Shift
6

The percentage dissociation of a salt (MX3) solution at given temperature (van't Hoff factor i = 2) is % (Nearest integer)

JEE Main 2025 (Online) 7th April Morning Shift
7

Liquid A and B form an ideal solution. The vapour pressures of pure liquids A and B are 350 and 750 mm Hg respectively at the same temperature. If xA and xB are the mole fraction of A and B in solution while yA and yB are the mole fraction of A and B in vapour phase, then,

  1. (xA - yA) < (xB - yB)
  2. xAxB = yAyB
  3. xAxB < yAyB
  4. xAxB > yAyB
JEE Main 2025 (Online) 7th April Evening Shift
8

Match List - I with List - II. Choose the correct answer from the options given below :

  1. A-III, B-I, C-IV, D-II
  2. A-III, B-IV, C-I, D-II
  3. A-II, B-I, C-IV, D-III
  4. A-II, B-IV, C-I, D-III
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9

XY is the membrane/partition between two chambers 1 and 2 containing sugar solutions of concentration c1 and c2 (c1 > c2) mol L-1. For the reverse osmosis to take place identify the correct condition. (Here p1 and p2 are pressures applied on chamber 1 and 2.) [figure] Choose the correct answer from the options given below:

  1. A and C Only
  2. A and D Only
  3. B and D Only
  4. C Only
JEE Main 2025 (Online) 4th April Morning Shift
10

Given below are two statements: In the light of the above statements, choose the most appropriate answer from the options given below :

  1. Statement I is correct but Statement II is incorrect
  2. Both Statement I and Statement II are incorrect
  3. Statement I is incorrect but Statement II is correct
  4. Both Statement I and Statement II are correct
JEE Main 2025 (Online) 4th April Evening Shift
11

Sea water, which can be considered as a 6 molar (6 M) solution of NaCl, has a density of 2 g mL-1. The concentration of dissolved oxygen (O2) in sea water is 5.8 ppm. Then the concentration of dissolved oxygen (O2) in sea water, in terms of molality, is x 10-4 m. x = . (Nearest integer) Given: Molar mass of NaCl is 58.5 g mol-1 Molar mass of O2 is 32 g mol-1

JEE Main 2025 (Online) 4th April Evening Shift

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