Given that the abundances of isotopes 54Fe, 56Fe and 57Fe are 5%, 90% and 5% respectively, what is the average atomic mass of iron?

The average atomic mass (A) is calculated using the formula:
¯A = Σ(Aᵢxᵢ) / Σxᵢ
where Aᵢ is the mass of each isotope and xᵢ is its abundance.
In this case:
¯A = (54 × 0.05) + (56 × 0.90) + (57 × 0.05)
¯A = 2.7 + 50.4 + 2.85
¯A = 55.95
Therefore, the average atomic mass of iron is 55.95