Question

If the ionic radii of ${K^ + }$ and ${F^ - }$ are nearly same (i.e. $1.34{A^\circ }$), then the atomic radii of K and F respectively are:
A. $1.34{A^\circ }$, $1.34{A^\circ }$
B. $0.72{A^\circ }$, $1.96{A^\circ }$
C. $1.96{A^\circ }$, $0.72{A^\circ }$
D. $1.96{A^\circ }$, $1.34{A^\circ }$

Answer 1

Atomic and ionic radii are used to denote the distance of an atom/ion from the nucleus. Ionic radii are the distance between the nucleus and valence shell electrons of ions whereas atomic radii are the distance between the nucleus and valence shell electrons of an atom.

Complete step by step answer:
Generally, the size of atomic radii is greater than ionic radii of positive ions and the size of atomic radii is less than ionic radii of negative ions.
The ionic radii and atomic radii won't be the same. And also the radii of positive and negative ions must be different.
It is known that the size of atomic radii is greater than the ionic radii of a positive ion. So the atomic radii of K must be greater than $1.34{A^\circ }$. Thus, the atomic radii of won’t be equal to $0.72{A^\circ }$
In this option, the atomic radii of K are given as $1.96{A^\circ }$ and it is known that the size of atomic radii is greater than ionic radii of positive ions and this condition is satisfied. The atomic radii of F is given as $0.72{A^\circ }$. It is known that the size of atomic radii is less than ionic radii of negative ions and thus, this condition is also satisfied.
In this option, the atomic radii of K are given as $1.96{A^\circ }$ and it is known that the size of atomic radii is greater than ionic radii of positive ions and this condition is satisfied. But the atomic radii of F is $1.34{A^\circ }$ which is the value for ionic radii. Generally, ionic radii and atomic radii won't be the same.
Thus, the atomic radii of K and F respectively are $1.96{A^\circ }$, $0.72{A^\circ }$

So, the correct answer is Option C.

Note: The size of sodium atom (Na) is greater than the size of sodium ion ($N{a^ + }$) because $N{a^ + }$ ion has lost its one electron and it leads to decrease in size. Similarly, the size of chlorine atom (Cl) is smaller than chlorine ion ($C{l^ - }$) because one electron gets added in $C{l^ - }$ and it leads to increase in size.