**i. Principal Quantum Number (n):** It defines the shell. It determines the size and energy of the orbit. The values of n are: n = 1, 2, 3, ……

**ii. Azimuthal Quantum Number (l):** It defines the shape of the orbital. For the given value of "n", the possible values of "l" are l = 0, 1, 2, 3, …. Each orbital is represented by the letters s, p, d, f.

**iii. Magnetic Quantum Number (ml):** It gives the spatial orientation of the orbital. For any value of l,ml can have (2l + 1) values ranging from –l to +

**iv. Spin Quantum Number(ms): **It refers to the spin of the electron. The value of spin quantum no are +1/2 and -1/2.