No. of different transition from n= n1 to n= n2 is given by n1Cn2 So for 6 different wavelength, no. of different transition = 6 n1Cn2=6 then n1 = n2 +3 If n is the principal quantum number of energy level corresponding to energy X, the principal quantum number of energy level Y is (n + 3) as it emit 6 wavelengths. Now Energy of an orbit is directly proportional to square of the orbit no.(principlal quantum no.)