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Solutions · Question 36

JEE Main 2025 (Online) 29th January Morning ShiftMCQMedium📈 Topic in 19% papers+4−1
1

1.24 g of AX2 (molar mass 124 g mol-1) is dissolved in 1 kg of water to form a solution with boiling point of 100.0156°C, while 25.4 g of AY2 (molar mass 250 g mol-1) in 2 kg of water constitutes a solution with a boiling point of 100.0260°C. Kb(H2O) = 0.52 kg mol-1 Which of the following is correct?

  1. AX2 and AY2 (both) are completely unionised.
  2. AX2 and AY2 (both) are fully ionised.
  3. AX2 is completely unionised while AY2 is fully ionised.
  4. AX2 is fully ionised while AY2 is completely unionised.

Answer

(4) AX2 is fully ionised while AY2 is completely unionised.

Solution

Tb = i Kb m i = TbKb m

For AX2: m = 1.24/1241 = 0.01 mol kg-1, Tb = 100.0156 - 100 = 0.0156 K

i = 0.01560.52 0.01 = 3

AX2 A2+ + 2X- is complete, i.e. AX2 is fully ionised.

For AY2: m = 25.4/2502 = 0.10162 = 0.0508 mol kg-1, Tb = 0.0260 K

i = 0.02600.52 0.0508 = 0.02600.0264 1

AY2 is completely unionised.

Answer: (4)

JEE Main 2025 (Online) 29th January Morning Shift

Keep practising — Solutions

2

If A2B is 30% ionised in an aqueous solution, then the value of van't Hoff factor (i) is 10-1.

JEE Main 2025 (Online) 29th January Morning Shift
3

What is the freezing point depression constant of a solvent, 50 g of which contain 1 g non-volatile solute (molar mass 256 g mol-1) and the decrease in freezing point is 0.40 K?

  1. 4.43 K kg mol-1
  2. 3.72 K kg mol-1
  3. 5.12 K kg mol-1
  4. 1.86 K kg mol-1
JEE Main 2025 (Online) 28th January Morning Shift
4

Assume a living cell with 0.9% (w/w) of glucose solution (aqueous). This cell is immersed in another solution having equal mole fraction of glucose and water. (Consider the data upto first decimal place only) The cell will :

  1. shrink since solution is 0.45% (w/w) as a result of association of glucose molecules (due to hydrogen bonding)
  2. shrink since solution is 0.5% (w/w)
  3. show no change in volume since solution is 0.9% (w/w)
  4. swell up since solution is 1% (w/w)
JEE Main 2025 (Online) 28th January Evening Shift

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