JEE Main · 2023 · Shift-IeasyMOLE-098

The number of molecules and moles in 2.8375 litres of O2 at STP are respectively:

Some Basic Concepts (Mole Concept) · Class 11 · JEE Main Previous Year Question

Question

The number of molecules and moles in 2.83752.8375 litres of \ceO2\ce{O2} at STP are respectively:

Options
  1. a

    7.527×10237.527 \times 10^{23} and 0.125mol0.125\,\text{mol}

  2. b

    7.527×10227.527 \times 10^{22} and 0.250mol0.250\,\text{mol}

  3. c

    1.505×10231.505 \times 10^{23} and 0.250mol0.250\,\text{mol}

  4. d

    7.527×10227.527 \times 10^{22} and 0.125mol0.125\,\text{mol}

Correct Answerd

7.527×10227.527 \times 10^{22} and 0.125mol0.125\,\text{mol}

Detailed Solution

🧠 Two questions, one mole count First find the moles. Then multiply by NAN_A for molecules. Use the modern STP molar volume 22.7L/mol22.7\,\text{L/mol} (post-1982 IUPAC standard at 1bar1\,\text{bar}).

🗺️ Two clean steps Moles =2.8375/22.7=0.125mol= 2.8375 / 22.7 = 0.125\,\text{mol}. Molecules =0.125×6.022×10237.527×1022= 0.125 \times 6.022 \times 10^{23} \approx 7.527 \times 10^{22}.

⚠️ STP version trap The number 2.83752.8375 is exactly 22.7/822.7 / 8. That is your hint to use 22.722.7, not 22.422.4. Using 22.422.4 here gives messy decimals that don't match any option.

Answer: (d)\boxed{\text{Answer: (d)}}

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