It is denoted by n. It tells us about the energy level or shell in which the electron is present. The value of n can be 1,2,3,4…….etc. but it cannot be zero. It gives us the information about the average distance of electrons from the nucleus, determines the energy of electron in hydrogen atom and hydrogen like atoms. It also gives us the information about the maximum number of electrons that a shell can have by using the formula 2n2.