A bottle contains 6.23 g of copper turnings. The mass of a length of magnesium ribbon is 6.23 g. Are there more copper atoms or more magnesium atoms present?

Moles = mass (g) / molar mass (g/mol)

Molar mass of copper = 63.5 g/mol

Molar mass of magnesium = 24.3 g/mol

Moles of copper = 6.23 g / 63.5 g/mol = 0.098 mol

Moles of magnesium = 6.23 g / 24.3 g/mol = 0.256 mol

according to the Avogadro constant,

1 mol = 6.022 x 10²³

Hence,

atoms of copper = 0.098 x 6.022 x 10²³ = 5.902 x 10²²

atoms of magnesium = 0.256 x 6.022 x 10²³ = 15.416 10²²

Hence magnesium ribbon has more atoms.