Question

k+,Ar,Cl-.which is largest give reason?

Answer 1

Ar>cl->k+
Reason ;
All the noble gases are largest(in terms of radius) in their respective period. Because of their gaseous nature. (and hence vanderwall. Radius is considered)
Next among k+ and cl-; anion is bigger because they receive an electron and hence repulsive forces act.(this reasoning is valid only if the elements to be compared are in same period)