Question

Number of atoms in $558.5$ gram Fe is:

[Atomic mass of $Fe=55.85u$]

• A. twice that of 60 g carbon
• B. $6.023\times {10}^{22}$
• C. half that in $8$g He
• D. $558.5\times 6.023\times {10}^{23}$

Answer 1

Answer: (A)

twice that of 60 g carbon

Number of moles of Fe atoms = $\frac{Mass}{Atomicmass}$ $=\frac{558.5}{55.85}=10$

558.5 g of Fe corresponds to 10 moles of Fe and has $10N_A$ atoms of Fe.

Option A - 12 g of carbon means Avogadro's number, therefore, 60 g of carbon means, 5 moles of carbon and thus contains $5\times N_A$ atoms, twice of this equals $10N_A$ atoms.

Option B - $\frac{N_A}{10}$ atoms.

Option C - 8 g of He corresponds to 2 moles of He and thus, contains $2N_A$ atoms, half of the atoms will be $N_A$ atoms of He.

So, option A only corresponds to number of atoms in 558.5 g Fe, i.e. $10N_A$ atoms.