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Friday, 9 October

JEE Main 2026 · ChemistryMultiple choiceSingle correctMediumCalculation

JEE Main 2 April 2026, Shift 1, Chemistry Q55

Question 55 of 75 in this shift, Chemistry question 5 of 25, Section A.

19.519.5 g of fluoro acetic acid (molar mass =78 g mol−1=78\ \mathrm{g\ mol^{-1}}) is dissolved in 500500 g of water at 298298 K. The depression in the freezing point of water was 1∘1^\circC. What is KaK_a of fluoro acetic acid ? (For water, Kf=1.86 K kg mol−1K_f=1.86\ \mathrm{K\ kg\ mol^{-1}}). Assume molarity and molality to have same values.
  1. (1)10−610^{-6}
  2. (2)4×10−44\times10^{-4}
  3. (3)3×10−53\times10^{-5}
  4. (4)3×10−33\times10^{-3}Official answer

Official answer

Option 4

NTA final key.

Chapter
Solutions
Topic
Colligative Properties
Idea tested
Calculating Ka from Freezing Point Depression

Same idea in other shifts

Asked 3× in all
  1. 8 Apr 2025, Shift 2 · Q53HA(aq)⇌H+(aq)+A−(aq)\mathrm{HA(aq) \rightleftharpoons H^+(aq) + A^-(aq)} The freezing point depression of a 0.1 m aqueous solution of a monobasic weak acid…MediumSingle correct
  2. 29 Jun 2022, Shift 1 · Q831.2 mL of acetic acid is dissolved in water to make 2.0 L of solution. The depression in freezing point observed for this strength of acid…MediumNumerical value

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.