Answer :
First calculate the moles of selenium by multiplying the mass x molar mass
90.2 × 78.96 = 7122.2 moles
Number of moles multiplied by avogadros number gives number of atoms
7122.2 × 6.022 × 10^{23} = 4.289×10^{27} atoms
90.2 × 78.96 = 7122.2 moles
Number of moles multiplied by avogadros number gives number of atoms
7122.2 × 6.022 × 10^{23} = 4.289×10^{27} atoms
