As we know that mole is unit of measuring amount or number of atoms, it is an absolute number. One mole is equal to 6.022 X 10^23 atoms. In given problem, we are given 9.03 X 10^24 atoms of mercury. So, number of moles in the given mercury sample will be (9.03 X 10^24)/(6.022 X 10^23). That is, 14.995 ~ 15 moles