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NDA 2020 GAT · General Knowledge · Mole Concept and States of Matter · hard

The number of oxygen atoms in 0.5 mole of oxygen gas (O2) is (Avogadro number = 6.022 x 10^23)

Single correct option

The number of oxygen atoms in 0.5 mole of oxygen gas (O2) is (Avogadro number = 6.022 x 10^23)
  1. A. 6.022 x 10^23
  2. B. 3.011 x 10^23
  3. C. 1.2044 x 10^24
  4. D. 6.022 x 10^22
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Answer: (A) 6.022 x 10^23

0.5 mole of O2 contains 0.5 x 6.022 x 10^23 molecules. Each molecule has two atoms, so the number of atoms is 2 x 3.011 x 10^23 = 6.022 x 10^23. The value 3.011 x 10^23 counts molecules only, which is the trap of forgetting that oxygen is diatomic.
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Original question written in the NDA 2020 GAT pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake