Spin quantum number is fourth set of quantum number. It is indicated the orientation of the intrinsic angular momentum of electron in an atom. It is denoted by ms . There are only two values for s + ½ and s - ½ . These are also referred to as 'spin up' and 'spin down'. The electron in the atom rotates not only around the nucleus but also around its own axis and two opposite direction of rotation are possible ( clockwise and anticlock wise).