Answer
The number of atoms in a human body is about $6\times10^{27}$ atoms.
Work Step by Step
The most common type of atoms in the human body is oxygen, carbon, hydrogen and nitrogen .
About 65.0% of the mass of our body is oxygen , 18.5% is carbon , 9.5% is hydrogen , 3.2% is nitrogen and the rest are other atoms.
Now, the atomic masses are :
Oxygen=15.999u , Carbon=12.011u , Hydrogen = 1.008u , Nitrogen=14.007u
where u=atomic mass unit=$1.661\times10^{-27}$
Assuming that the mass of the person be 70kg .The approximate number of atoms in the human body is obtained as
Number of atoms=$\frac{70\times\frac{65.0}{100}}{15.999\times1.661\times10^{-27}}+\frac{70\times\frac{18.5}{100}}{12.011\times1.661\times10^{-27}}+\frac{70\times\frac{9.5}{100}}{1.008\times1.661\times10^{-27}}+\frac{70\times\frac{3.2}{100}}{14.007\times1.661\times10^{-27}}$
$\approx6\times10^{27}$
Therefore ,the number of atoms in a human body is about $6\times10^{27}$ atoms.
