(a) What is an oc

(a) Octet means the presence of 8 electrons in the outermost shell of an atom which means the atom is stable and has the electron arrangement of inert gas. Every atom wants to attain stability so they combine with one another and by gaining or losing or mutually sharing electrons they reach the octet state.

(b) Structure of magnesium whose atomic number is 12- 2, 8, 2

Structure of phosphorus whose atomic number is 15- 2, 8, 5