Which of the following has the maximum number of atoms?

(A) 0.5 g atoms of Cu (B) 0.635 g of Cu

(C) 0.25 moles of Cu atoms (D) 1 g of Cu

The molar mass of copper is 63.5g. Thus there are 6.023 X 10²³ atoms of copper in 63.5g of copper. So

63.5g of copper = 6.023 X 10²³ atoms of copper

1g of copper = (6.023 X 10²³ / 63.5) atoms of copper

So 0.5g of copper = (6.023 X 10²³ X 0.5) / 63.5 atoms of copper

= 4.742 X 10²¹ atoms of copper

Similarly, the number of atoms in 0.635g of copper and 1g of copper come out to be  6.023 X 10²¹ and 9.485 X 10²¹ respectively. However, for 0.25 moles of copper, we will have

 1 mole of copper = 6.023 X 10²³ atoms of copper

 0.25 moles of copper = 0.25 X 6.023 X 10²³ atoms of copper

 = 1.506 X 10²³ atoms of copper

So, the correct answer is (c) 0.25 moles of copper.