The number of electrons lost, gained or shared by an atom of an element is known as ………………………

Electro valency - The number of electrons of an element that take part in a chemical reaction to attain nearest noble gas configuration is known as its valency

For example,

Sodium (${}_{11}Na$) - 2, 8, 1. Sodium donates its outermost electron to attain the configuration of nearest noble gas . So its valency is 1

Oxygen (${}_{8}O$) - 2,6. Oxygen accept two electrons to attain nearest noble gas configuration. So its valency is 2 .

Therefore, the number of electrons lost, gained or shared by an atom of an element is known as electro valency.