Variable valency is generally shown by-

Options

A. `s-`block elements
B. `p-`block elements
C. Transition elements
D. All elements in periodic table

Explanation

One of the most striking features of the transition elements, is that they exhibit variable valency. The variable valency occurs to some extent in the `p-`block elements also. In this case the valency changes usually in units of two. Some example are `SnCl_(2),SnCl_(4),PCl_(3),PCl_(5) etc`. But in transition elements the valency changes in one unit `e.g Cu^(+),Cu^(+2),Fe^(+2),Fe^(+3) etc`.