Question

What do you understand by valency ? What are the valancies of boron and xenon

Answer 1

In chemistry, the valence or valency of an element is a measure of its combining power with other atoms when it forms chemical compounds or molecules.
Valency is the combining capacity of an element.

Valency is the number of electrons that a neutral atom of an element loses or gains to have noble gas electronic configuration (to become stable).

Boron

-3, +3

Xenon

0