Define valency by taking examples of silicon and oxygen.

Explanation

The valency of an element is defined as the number of electrons lost, gained or shared by on atom of the element to achieve the nearest inert gas electron configuration (of having 8 electrons in the outermost shell (or 2 electrons if the outermost shell is K shell)
(i) Valency of silicon. The atomic number of silicon is 14, so it has 14 electrons in its atom. The electronic configuration of silicon atom will be `underset("2, 8, 4")("K L M")` Thus, the silicon atom has 4 electrons in its outermost