Which is more covalent $ AgCl $ or $ KCl $ .

Hint: First we know that the covalent character depends upon the size of the cation and size of anion. Also, the covalent character is inversely proportional to the electronegativity difference and similar atoms have the least electronegativity difference. Therefore, they have the maximum covalent character. Using Fajan’s rule we find which is more covalent.

Complete answer:
The ability of a cation to distort an anion is known as its polarization power and the tendency of the anion to become polarized by the cation is known as its polarizability. Smaller is the size of the cation and higher will be its charge density, which means greater concentration of charge on a smaller area. Therefore, the polarizing power of a cation is inversely proportional to its size. Hence the covalent character is proportional to the polarizing power of a cation.
Fajan’s rule states “Larger the cation size lesser is the covalent character.” $ A{g^ + } $ cation is generally bigger and larger than $ {K^ + } $ atoms. So, $ AgCl $ has less covalent character than $ KCl $ .
Hence $ KCl $ is more covalent than $ AgCl $ .

Note:
In covalent bonds, atoms share electrons, whereas in ionic bonds atoms transfer electrons. The reaction components of covalent bonds are electrically neutral, whereas for ionic bonds they are both charged. An anion is an ion that has gained one or more electrons, acquiring a negative charge. A cation is an ion that has lost one or more electrons, gaining a positive charge.
If the degree of polarization is quite small, an ionic bond is formed, while if the degree of polarization is large, a covalent bond is formed.