Question

The figure shows a sample of H-atoms having electron revolving in higher orbit 'n'. If this electron makes transition from this orbit 'n' to ground state, number of paschen lines emtted are.

Answer 1

n-3

Answer 2

The Paschen series corresponds to transitions to the $n=3$ energy level. For Paschen lines to be emitted from an initial orbit 'n', the electron must transition from an orbit $k$ to $n=3$, where $3 < k \le n$. The possible initial orbits are $4, 5, \dots, n$. The number of such orbits is $n - 4 + 1 = n-3$. This is valid for $n \ge 4$.