Question

The species Ar, K+ and Ca2+ contain the same
number of electrons. In which order do their radii
increase ?
(1) Ca2+ < Ar < K+ (2) Ca2+ < K+ < Ar
(3) K+ < Ar < Ca2+ (4) Ar < K+ < Ca2+
Please explain the answer thoroughly by solving every option.

Answer 1

they are known as isoelectronic species because they contain same number of electrons

in isoelectronic species as positive charge increases size decreases

potassium ion has 19p&18e
calcium ion has 20p& 18 e
argan has 18p&18e
protons increases means attraction between nucleus & valence electrons increases so size decreases
option 2 is correct

Answer 2

OPTION 2 IS THE CORRECT ONE.........