What mass of copper, contains the same number of atoms as 50.0 g of silicon?
1. Divide 50.0g of Si by the atomic mass of Si. That will give you the moles of silicon.
2. Equal moles of any two elements contain equal numbers of atoms. Based on that, multiply the previous answer by the atomic mass of copper to get the number of grams of copper with the same number of atoms as 50.0 grams of silicon.