Energy of a spectral line in hydrogen depends on transition:
\[ E = 13.6 \left( \frac{1}{n_f^2} - \frac{1}{n_i^2} \right) \]
Lower final level → greater energy.
Identify transitions:
Paschen series → nf = 3
Balmer series → nf = 2
Brackett series → nf = 4
A. First Paschen line: 4 → 3
C. Third Paschen line: 6 → 3
B. Second Balmer line: 4 → 2
D. Fourth Brackett line: 8 → 4
Energy increases when:
• Final level is smaller
• Initial level is higher (for same series)
Lowest energy → Brackett (nf = 4)
Then Paschen (nf = 3)
Highest energy → Balmer (nf = 2)
Within Paschen:
6 → 3 has more energy than 4 → 3
Ascending order:
D < A < C < B
Correct Option: C