Verified Solution • 2025–26 Session moderate

QJEEM25Ch8c6c: JEE Main 2025 Chemistry - Class 12 JEEM25Ch8c6c Solution: 1.24 g of AX 2 (molar mass 124 g mol −1 ) is dissolved in 1 kg…

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 100.015°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?

Multiple Choice Options

  • A AX2 and AY2 (both) are completely unionised.
  • B AX2 and AY2 (both) are fully ionised.
  • C AX2 is completely unionised while AY2 is fully ionised.
  • D AX2 is fully ionised while AY2 is completely unionised.

Step-by-Step Verified Solution

For AX2:−ΔTb=Kb×m×i\mathrm{AX}_2:-\Delta \mathrm{T}_{\mathrm{b}}=\mathrm{K}_{\mathrm{b}} \times \mathrm{m} \times \mathrm{i}

0.0156=0.52×0.011×iAX20.0156=0.52 \times \frac{0.01}{1} \times \mathrm{i}_{\mathrm{AX}_2}

⇒iAX2=3⇒\Rightarrow \mathrm{i}_{\mathrm{AX}_2}=3 \Rightarrow complete ionisation

For AY2:−ΔTb=Kb×m×i\mathrm{AY}_2:-\Delta \mathrm{T}_{\mathrm{b}}=\mathrm{K}_{\mathrm{b}} \times \mathrm{m} \times \mathrm{i}

0.026=0.52×0.0508×iAY20.026=0.52 \times 0.0508 \times \mathrm{i}_{\mathrm{AY}_2}

⇒iAY2≃1∴\Rightarrow \mathrm{i}_{\mathrm{AY}_2} \simeq 1 \therefore complete unionisation

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