:Quantum Number -It can be defined as set of four numbers which helps in KNOWING all the information of an electron.Types of Quantum Number -Principal Quantum no.They are represented as 'n'. They are used to explain the main lines of a spectrum. It tells about the main shell in which electron is present. It also tells about approximate distance between the electron and the nucleus and the energy of the shell. The maximum number of electrons present in a shell is represented by 2n². The shells are card as K, L, M, N ....Azimuthal Quantum no.They are represented as 'l'. They are used to explain fine structure of LINE spectrum. It tells US about the number of subshells present in the main shells. It also tells about the relative energies of the subshells and the shape of the orbital. For a given value of n, l can have n values ranging from 0 to n-1. If l = 0, s-subshell; l = 1, p-subshell; l = 2, d-subshell; l = 3, f-subshell; l = 4, g-subshell; l = 5, h-subshell.Magnetic Quantum no.They are represented by 'm or m_l'. They are used to explain splitting of lines in a magnetic field. They TELL about number of orbitals present in a subshell. For a particular value of l of a subshell, m = -l to l including 0. Spin Quantum no.They are represented as 's or m_s'. They are used to explain the magnetic properties of substances. It tells about the direction of electron spin. For a particular value of m (orbital), s = +½, -½. The two arrows pointing upwards and downwards are used to indicate two spin STATES that is spin up and spin down.