Which one of the following has different number of molecules? (All kept at normal temperature and pressure)

Question

Question

This question was previously asked in

NDA (Held On: 18 Sept 2016) General Ability Test Previous Year paper

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Answer 1

The correct answer is option 4 i.e. 2 grams of carbon.

Number of moles

The number of moles can be calculated by Mass (g) divided by Molecular mass.
We know the same number of moles have the same number of molecules or atoms.
3 grams of Hydrogen = 1.5 moles, because the molecular mass of Hydrogen is 2.
48 grams of Oxygen= 1.5 moles, because the molecular mass of Oxygen is 32.
42 grams of Nitrogen = 1.5 moles, because the molecular mass of Nitrogen is 28.
2 grams of carbon = 0.167 moles, because the molecular mass of carbon is 14.
Hence option 4 is correct.