JEE Main 2021 · ChemistryNumerical answerNumerical valueEasyCalculation

JEE Main 18 March 2021, Shift 1, Chemistry Q51

Question 51 of 90 in this shift, Chemistry question 21 of 30, Section B.

Complete combustion of 3 g of ethane gives

x\times10^{22}

molecules of water. The value of

x

is __________. (Round off to the Nearest Integer). [Use :

N_A = 6.023\times10^{23}

; Atomic masses in u : C : 12.0 ; O : 16.0 ; H : 1.0]

Official answer

NTA final key.

Chapter: Some Basic Concepts of Chemistry
Topic: Mole Concept
Idea tested: Mole and Avogadro Calculations

Same idea in other shifts

Asked 5× in all

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6 Apr 2026, Shift 2 · Q51Which of the following contain the same number of atoms ? (Given : Molar mass in g mol $^{-1}$ of H, He, O and S are 1, 4, 16 and 32…EasyOther
8 Apr 2026, Shift 2 · Q51Match List - I with List - II. List - I (Mass of substance) | List - II (Number of atoms) A. 1.8 mg water | I.…EasyMatch the list
3 Apr 2025, Shift 1 · Q51Among $10^{-9}$ g (each) of the following elements, which one will have the highest number of atoms? Element: Pb, Po, Pr and PtEasySingle correct

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.