Question

Which of the following has the largest ionic radius?
A. ${\text{C}}{{\text{s}}^ + }$
B. ${\text{L}}{{\text{i}}^ + }$
C. ${\text{N}}{{\text{a}}^ + }$
D. ${{\text{K}}^ + }$

Answer 1

The distance from the centre of the nucleus of the atom to the boundary of the shells is known as the ionic radius. The trend in ionic radius is as follows: The ionic radius decreases from left to right across the period. The ionic radius increases down the group.

Complete answer:
The ions given to us are ${\text{C}}{{\text{s}}^ + }$, ${\text{L}}{{\text{i}}^ + }$, ${\text{N}}{{\text{a}}^ + }$ and ${{\text{K}}^ + }$.
All these ions belong to the group IA of the periodic table.
In the periodic table, the elements are arranged in an increasing order of their atomic numbers.
As we move from top to bottom in the periodic table, the atomic number of the elements increases. By this definition, the atomic number increases in the order ${\text{L}}{{\text{i}}^ + }$ < ${\text{N}}{{\text{a}}^ + }$ < ${{\text{K}}^ + }$ < ${\text{C}}{{\text{s}}^ + }$.
As we move from top to bottom in the periodic table, the ionic radius of elements keeps on increasing. This is because as one electron is removed from the valence shell of the atom, the effective nuclear charge on the valence shell decreases. thus, ionic radius increases.
Thus, the ionic radius of ${\text{C}}{{\text{s}}^ + }$ is the largest.

**Thus, the correct option is (A) ${\text{C}}{{\text{s}}^ + }$.

Note:**
The ionic radius is the radius of an ion. An ion can be positively or negatively charged. A positively charged ion is formed when electrons are removed from a neutral atom. A negatively charged ion is formed when electrons are added from a neutral atom.