Calculate the number of atoms in $120 \, g$ of calcium and $120 \, g$ of iron. Which one has more number of atoms and what is the difference? (Given: atomic mass of calcium $= 40 \, u$ and iron $= 56 \, u$)

• A
  $18.066 \times 10^{23}$ atoms of $Ca$,$12.887 \times 10^{23}$ atoms of $Fe$; $Ca$ has more; difference $= 5.179 \times 10^{23}$
• B
  $12.044 \times 10^{23}$ atoms of $Ca$,$18.066 \times 10^{23}$ atoms of $Fe$; $Fe$ has more; difference $= 6.022 \times 10^{23}$
• C
  $18.066 \times 10^{23}$ atoms of $Ca$,$12.887 \times 10^{23}$ atoms of $Fe$; $Fe$ has more; difference $= 5.179 \times 10^{23}$
• D
  $12.044 \times 10^{23}$ atoms of $Ca$,$12.887 \times 10^{23}$ atoms of $Fe$; $Ca$ has more; difference $= 0.843 \times 10^{23}$