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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. K_b(H2O) = 0.52 K kg mol^-1 Which of the following is correct ?

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

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

Solution

The boiling point elevation indicates the number of particles in solution. AX2, with a lower molar mass and higher boiling point elevation, suggests it is fully ionised, contributing more particles. In contrast, AY2, with a higher molar mass and lower boiling point elevation, indicates it is completely unionised, contributing fewer particles.

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