Question

In a sample of H-atoms, electrons are de-excited from its 4th excited state to the ground state. Which is an incorrect statement?

• A. No line is observed in P-fund series
• B. A total 12 lines is observed in the spectrum
• C. A total of 4 lines in UV region and 3 lines in visible region are observed
• D. One line observed in the Brackett series

Answer 1

The correct option is B A total 12 lines is observed in the spectrum

4th excited belongs to $n=5$
As, all lines of P-fund terminate at $n=5$ from energy levels above. So, here no line observed in P-fund series.
Total number of possible lines observed $=\frac{(n_2-n_1)(n_2-n_1+1)}{2}[\because n_1=1;n_2=5]$
$=\frac{(5-1)(5-1+1)}{2}=10$

4 lines corresponding to following transition observed in UV region.
$5\to 1;4\to 1;3\to 1;2\to 1$

3 lines observed in Balmer series corresponding to following transtion:
$5\to 2;4\to 2;3\to 2$

Only one line observed in Brackett series for the transition $5\to 4$.