Along the period `(rarr)` atomic`//`ionic radii and metallic character decreases while `IE`, `EN` , non-metallic character and oxidising power increases. Down the group `(darr)`, atomic`//`ionic radii, metallic character and reducing character increase while `IE` and `EN` decrease. However, `Delta_(eg)H^(ɵ)` becomes less negative down a group but more negative along a period.
In which of the following pairs, both species have nearly the same size ? (more than one correct)

Options

A. `Mg^(2+), Al^(3+)`
B. `K^(o+)`, `F^(ɵ)`
C. `Li^(o+)`, `Mg^(2+)`
D. `Rb^(o+), O^(2-)`

Answer

B, C, D

Explanation

a. `Mg^(2+)` and `Al^(3+)` are isoelectronic, so their ionic sizes will be different.
`Mg^(2+) = 65` and `Al^(3+) = 50 pm`
So, the answer which have same sizes are b, c and d.
b. `K^(o+) = 133 p m, and F^(ɵ) = 136p m`, nearly the same size.
c. `Li^(o+) = 60 p m`, and `Mg^(2+) = 65 p m`, nearly the same size due to diagonal relationship.
d. `Rb^(o+) = 148 p m`, and `O^(2-) = 140 p m`, nearly the same size.
Note : To solve such trickly questions, it is advised to check the isoelectronic species only because they will have different sizes and others may have same size.