The only `e^-` in the H-atom resides under ordinary conditions on the first orbit when energy is supplied, the `e^-` moves to higher energy shells depending upon the amount of energy absorbed. When an e emits energy i.e., the `e^-` returns to the lowest energy state, from this Lyman, Balmer, Paschen, Bracket, Pfund series are there, so different spectral lines in the spectra of atoms correspond to different transitions of `e^-` s from higher to lower energy levels:
The ratio of number of spectral lines obtained when an `e^-` s jumps from `7^(th)` to ground to `6^(th)` to `3^(rd)`

Options

A. 7
B. 3.5
C. 10
D. 2.5

Answer

B

Explanation

Ratio of number of spectral lines
`implies ((7(7-1))/(2))/(((6-3)(6-3+1))/(2)) = (21)/6 = 3.5`