When electron jumps from higher orbit to lower orbit, then energy is radiated in the form of electro magnetic radiation and these radiations are used to record the emission spectrum Energy of electron may be calculated as E= (2pi^2 m_e Z^2 e^4)/(n^2 h^2) where m_e = rest mass of electron DeltaE = (E_(n_2)- E_(n_1)) = 13.6xxZ^2 xx [1/(n_1^2) - 1/(n_2^2)]eV per atom This equation was also used by Rydberg to calculate the wave number of a particular line in the spectrum. bar(upsilon) = 1/(lambda) = R_H Z^2 [1/(n_1^2) -1/n_2^2] m^(-1) Where , R_H = 1.1 xx 10^7 m^(-1) (Rydberg constant)For Lyman, Balmer, Paschen, Brackett and Pfund series the value of n_1 = 1,2,3,4,5 respectively and n_2 = oo for series limit, If an electron jumps from higher orbit n to ground state than number of spectral line will be ""^nC_2 . Ritz modified the Rydberg equation by replacing the rest mass of electron with reduced mass (mu). 1/(mu) = 1/(m_N) + 1/(m_e) , Here m_N mass of nucleus , m_e = mass of electron. The emission spectrum of He^+ involves transition of electron from n_1 ton_2 such that n_2 + n_1 = 8and n_2 - n_1 = 4 . What will be the total number of lines in the spectrum ?