Chemistry Q51 – JEE-MAIN 2026

Home Chemistry Basic ChemistryQuestion #45

Which 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 respectively) A. 2 g of O

_{2}

gas B. 4 g of SO

_{2}

gas C. 1400 mL of O

_{2}

at STP D. 0.05 L of He at STP E. 0.0625 mol of H

_{2}

gas Choose the correct answer from the options given below :

Clue 1 of 3: Moles and Avogadro's Number

To compare the number of atoms, first calculate the number of moles of each substance, then multiply by the number of atoms per molecule and Avogadro's number ( $N_{A}$ ).

🧠 Full Solution Path

Step 1: Calculate moles of substance for each option✦ Active

We need to calculate the number of moles of each given substance. Molar masses are given as H=1, He=4, O=16, S=32 g/mol. Molar volume at STP is $22.4 L/mol$ or $22400 mL/mol$ .

2 g of O_{2}

: Molar mass of

O_{2} = 2 \times 16 = 32 g/mol

. Moles of

O_{2} = \frac{2}{32} = \frac{1}{16} mol

. B.

4 g of {SO}_{2}

: Molar mass of

{SO}_{2} = 32 + 2 (16) = 64 g/mol

. Moles of

{SO}_{2} = \frac{4}{64} = \frac{1}{16} mol

. C.

1400 mL of O_{2} at STP

: Moles of

O_{2} = \frac{1400 mL}{22400 mL/mol} = \frac{14}{224} = \frac{1}{16} mol

. D.

0.05 L of He at STP

: Moles of He

= \frac{0.05 L}{22.4 L/mol} = \frac{5}{2240} = \frac{1}{448} mol

. E.

0.0625 mol of H_{2}

: Moles of

H_{2} = 0.0625 = \frac{1}{16} mol

Step 2: Calculate total moles of atoms for each option○ Expand

Now, we multiply the moles of each substance by the number of atoms present in one molecule of that substance to find the total moles of atoms. For monatomic He, it's 1 atom/molecule.

O_{2}

has 2 atoms/molecule. Moles of atoms

= \frac{1}{16} \times 2 = \frac{2}{16} = \frac{1}{8} mol

. B.

{SO}_{2}

has 3 atoms/molecule. Moles of atoms

= \frac{1}{16} \times 3 = \frac{3}{16} mol

. C.

O_{2}

has 2 atoms/molecule. Moles of atoms

= \frac{1}{16} \times 2 = \frac{2}{16} = \frac{1}{8} mol

. D. He has 1 atom/molecule. Moles of atoms

= \frac{1}{448} \times 1 = \frac{1}{448} mol

. E.

H_{2}

has 2 atoms/molecule. Moles of atoms

= \frac{1}{16} \times 2 = \frac{2}{16} = \frac{1}{8} mol

💡 Teacher's Secret Hint

Remember to account for the number of atoms in each molecule (e.g., O2 has 2 atoms, SO2 has 3 atoms, He has 1 atom).

Step 3: Compare the number of atoms○ Expand

Comparing the moles of atoms calculated in Step 2, we find that options A, C, and E all have $\frac{1}{8}$ mol of atoms. Therefore, they contain the same number of atoms ( $\frac{1}{8} N_{A}$ ).

✦ STEM Console utilizes AI models to generate step-by-step explanations and math clues. AI can make mistakes.

Chemistry Question 51 – JEE-MAIN 2026

Clue 1 of 3: Moles and Avogadro's Number

🧠 Full Solution Path