The species `Ar,K^(+)` and `Ca^(2+)` contain the same number of electrons. In which order do their radii increase ?

Options

A. `Ar lt K^(+) lt Ca^(2+)`
B. `Ca^(2+) lt Ar lt K^(+)`
C. `Ca^(2+) lt K^(+) lt Ar`
D. `K^(+) lt Ar lt Ca^(2+)`

Answer

C

Explanation

`Al ^(3+), K^(+)` and `Ca^(2+)` are isoelectronic i.e. with same number of electrons. 18. For isoelectronic species ionic radii decreases with increase in effective (relative) positive charge. Also Ar, K and Ca belong to the same period (3rd period).