Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56 u)?




To find which one has more atoms, we’ll find the number of moles of both.

Since 1 mole of any substance has the same number of atoms, the element having more number of moles will have more atoms .



Given mass of Na = m n =100g

Given mass of Fe = m f =100g


We know that,

Molar mass of a substance = Atomic mass of the substance (in g)



Molar mass of Na = M n = 23g

Molar mass of Fe = M f = 56g



Number of moles of a substance = Given mass of the substance / Molar mass of the substance

For Na, = m n /M n

             = 100/23

             ≈  4.34 moles


For Fe, = m f /M f

             = 100/56

             ≈  1.78 moles

Since, Number of moles of Na > Number of moles of Fe .

100g of Na will have more atoms than 100g of Fe .      

  1. Class 9
  2. Chapter 3 Class 9 - Atoms And Molecules (Term 2)

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CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo