Question

Give reasons:

The radius of Fe²⁺ (Z = 26) is less than that of Mn²⁺ (Z = 25).

Answer 1

1. Fe²⁺ has atomic number 26, Mn²⁺ has atomic number 25; Fe²⁺ has one more proton.
2. More protons in the  nucleus of Fe²⁺ attract electrons more strongly, pulling the electron cloud closer.
3. Both ions have the same charge (+2) and similar electron configurations, so the extra nuclear charge dominates.
4. Stronger nuclear attraction in Fe²⁺ results in a smaller ionic radius compared to Mn²⁺.

Thus, the radius decreases with increasing nuclear charge (Z) across the period for ions with the same charge.