Answer:
a) F⁻ < Cl⁻ < Br⁻
b) Mg²⁺ < Na⁺ < F⁻
c) Cr³⁺ < Cr²⁺
Explanation:
The ions in (a) part of the question belong to a halogen group. F, Cl, and Br are present in periods 2, 3, and 4 respectively. As we move down the group the size of atoms increases hence their ions will be in the same order. (ion from top to bottom of group 7)
The ions in (b) part of the question are isoelectronic. The relative size of such species can be estimated by the charge on their nucleus. Lower the nucleus charge greater will be the size of the ion.
Nuclear charge of Mg²⁺ = no. of protons = 12
Nuclear charge of Na⁺ = no. of protons = 11
Nuclear charge of F⁻ = no. of protons = 9
The ions in (c) part are the two oxidized states of chromium. In such cases, higher the number of nuclear charge smaller will be the ion.
