The radius of potassium ion

The radius of potassium atom is 0.203 nm. The radius of the potassium ion in nanometer will be :-
(1) 0.133
(2) 0.231
(3) 0.234 
(4) 0.251

Dear student,

The correct option is (1) 
Reason :   K $\stackrel{}{\to }$  K⁺  +  e^-1 
      Due to the formation of cation outermost electrons comes closer to the nucleus thus radius must be lower than 0.203 nm
  Regards