Number of atoms in 558.5 gram Fe (at. wt. of Fe = 55.85 g mol-1) is

Answer: (a) twice that in 60 g carbon

Moles of Fe \(= \dfrac{558.5}{55.85} = 10\) mol, so the number of atoms is \(10N_A = 6.023\times10^{24}\).

Check each option:

• (a) 60 g C \(= 60/12 = 5\) mol; twice this is 10 mol. Matches.
• (b) \(6.023\times10^{22}\) is only 0.1 mol.
• (c) 8 g He \(= 8/4 = 2\) mol; half of it is 1 mol.
• (d) \(558.5\times6.023\times10^{23}\) wrongly multiplies the mass (not the moles) by \(N_A\).