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NDA 2025 GAT · General Knowledge · Mole Concept and States of Matter · hard

The number of atoms present in 9 g of water is (N_A is Avogadro's number)

Single correct option

The number of atoms present in 9 g of water is (N_A is Avogadro's number)
  1. A. 1.5 N_A
  2. B. 0.5 N_A
  3. C. 3 N_A
  4. D. N_A
Show answer and solution

Answer: (A) 1.5 N_A

The molar mass of water is 18 g/mol, so 9 g is 0.5 mol of molecules, which is 0.5 N_A molecules. Each molecule has 3 atoms (2 hydrogen and 1 oxygen), so the number of atoms is 0.5 x 3 N_A = 1.5 N_A. The value 0.5 N_A counts molecules, not atoms.
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Original question written in the NDA 2025 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