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Saturday, 31 October

JEE Main 2021 · ChemistryMultiple choiceSingle correctMediumRecall

JEE Main 26 August 2021, Shift 1, Chemistry Q40

Question 40 of 90 in this shift, Chemistry question 10 of 30, Section A.

The conversion of hydroxyapatite occurs due to presence of F−\mathrm{F^-} ions in water. The correct formula of hydroxyapatite is :
  1. (1)[3 Ca3(PO4)2⋅CaF2][3\,\mathrm{Ca_3(PO_4)_2 \cdot CaF_2}]
  2. (2)[Ca3(PO4)2⋅CaF2][\mathrm{Ca_3(PO_4)_2 \cdot CaF_2}]
  3. (3)[3 Ca3(PO4)2⋅Ca(OH)2][3\,\mathrm{Ca_3(PO_4)_2 \cdot Ca(OH)_2}]Official answer
  4. (4)[3 Ca(OH)2⋅CaF2][3\,\mathrm{Ca(OH)_2 \cdot CaF_2}]

Official answer

Option 3

NTA final key.

Chapter
Environmental Chemistry
Topic
Environmental Chemistry
Idea tested
Drinking Water Standards: Fluoride Limits

Same idea in other shifts

Asked 3× in all
  1. 9 Apr 2024, Shift 1 · Q67The F−\mathrm{F^-} ions make the enamel on teeth much harder by converting hydroxyapatite (the enamel on the surface of teeth) into much…MediumSingle correct
  2. 25 Jul 2022, Shift 2 · Q72Match List I with List II. List I | List II A. Sulphate | I. Pesticide B. Fluoride | II. Bending of bones C. Nicotine | III. Laxative…MediumMatch the list

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 108 of the 174 JEE Main shifts held from 2017 to 2026.