Therefore it has orbital angular momentum given by :
Since, we’ve to calculated the total angular momentum. Now,
Due to electron spin 3p level consists of two sub-levels 3p(1/2) & 3p(3/2) corresponding to two values of j i.e. 1/2 and 3/2 respectively, while 3s level remains unsplitted.
Therefore, the transition 3p(3/2)»»3s(1/2) corresponds to Sodium D2 line, and transition 3p(1/2)»»3s(1/2) corresponds to sodium D1 lines.