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 11× in all

4 Apr 2026, Shift 2 · Q51The correct order of total number of atoms present in (A) 2 moles of cyclohexane (B) 684 g of sucrose (C) 90.8 L of dihydrogen at STP is:EasySingle correct
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
10 Apr 2023, Shift 1 · Q61The number of molecules and moles in 2.8375 litres of $\mathrm{O_2}$ at STP are respectivelyEasySingle correct
10 Apr 2023, Shift 2 · Q61Match List I with List II LIST I A. 16 g of $\mathrm{CH_4}$ (g) B. 1 g of $\mathrm{H_2}$ (g) C. 1 mole of $\mathrm{N_2}$ (g) D. 0.5 mol of…EasyMatch the list
26 Jul 2022, Shift 2 · Q61Hemoglobin contains 0.34% of iron by mass. The number of Fe atoms in 3.3 g of hemoglobin is (Given: Atomic mass of Fe is 56 u,…EasySingle correct
25 Jun 2022, Shift 1 · Q81The number of N atoms in 681 g of $\mathrm{C_7H_5N_3O_6}$ is $x \times 10^{21}$ . The value of $x$ is __________. (…EasyNumerical 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 108 of the 174 JEE Main shifts held from 2017 to 2026.