Which of the following has the largest number of atoms?

The number of moles of atoms in

Option A: $0.5 g$ atom of $Cu=0.5\times 6.023\times {10}^{23}=3.011\times {10}^{23}$ copper atoms

Option B: $0.635 g$ of $Cu=\frac{0.635}{63.5}\times 6.023\times {10}^{23}=6.023\times {10}^{21}$ copper atoms

Option C: $0.25$ mole of $Cu=0.25\times 6.023\times {10}^{23}=1.5\times {10}^{23}$ copper atoms

Option D: $6.35\times {10}^{20}$ amu of $Cu=\frac{6.023\times {10}^{23}}{63.5}\times 6.35\times {10}^{20}=0.6023\times {10}^{43}$ copper atoms

Hence, $0.5 g$ atom of $Cu$ has the largest number of atoms.

Therefore, option (A) is correct.