1g of Boron has the most number of atoms. This is simply because it has the highest number of moles.
Since 1 mole contain 6.22 × 10^23 atoms, the atom that has most moles closer to 1 will contain most atoms.
This in fact can be calculated from the fact that the number of moles equal mass divided by the atomic mass.
The mass here is equal I.e 1g and thus the dividing factor will be the atomic mass. The atom with the highest atomic mass here us thorium and thus will give the lowest number of moles. Zinc follows suit in that order with Boron at the top of the other and thus will contain the highest number of atoms.
