The sun is composed mostly of hydrogen. The mass of the sun is 2.0x10^30 kg, and the mass of a hydrogen atom is 1.67x10^-27 kg. Estimate the number of atoms in the sun.

We assume that the sun is all hydrogen for this or the amount other components are negligible. The calculations are as follows:

2.0x10^30 kg of sun x (1.67x10^-27 kg hydrogen atom / 1 kg of sun) = 3340 kg hydrogen atom

3340 kg hydrogen atom (1000 g / 1 kg) (1 mol H / 1.01 g H) = 3306930.693 mol H

3306930.693 mol H x (6.022 x 10^23 atoms / 1 mol) = 1.99 x 10^30 atoms H