Assuming that carbon occurs only in two isotopic forms $C^{12}$ and $C^{14}$; if isotopic distribution of  $C^{12}$ and  $C^{14}$ are 98.0% and 2.0% respectively, then the number of $C^{14}$ atoms in 12.04 g of carbon is

Atomic weight of carbon calculated on the basis of isotopic abundance = $(12\times 0.98)+(14\times 0.02)=12.04$ g $mol{e}^{-1}$(As per this question)

Number of mole of Carbon = $\frac{Mass of carbon 12.04 g}{Atomic weight of carbon 12.04 g mol{e}^{-1}}=1 mole$

No of atoms in 1 mole = $6.023\times {10}^{23}$

$C^{14}$ atoms constitute 2% of total atoms. So, number of $C^{14}$ atoms = $6.023\times {10}^{23}\times 0.02=1.20\times {10}^{22}$