Answer
He has the greatest number of atoms.
Work Step by Step
1 mole = $6.022 \times 10^{23}$ atoms
Number of mole = $\frac{mass}{molar mass} $
a) Number of mole = $\frac{10g}{4g/mol} = 2.5$ mole of He
b) Number of mole = $\frac{25g}{20g/mol} = 1.25$ mole of Ne
c) Number of mole = $\frac{115g}{131g/mol} = 0.114$ mole of Xe
He has the greatest number of moles, therefore, it has the greatest number of atoms as well.
