Which of the following series of transitions in the spectrum of hydrogen atoms falls in the visible region?

1. Brackett series

2. Lyman series

3. Balmer series

4. Paschen series

According to the Bohr Theory, which of the following transitions in the hydrogen atom will give rise to the least energetic photon?
1. n = 5 to n = 3
2. n = 6 to n = 1
3. n = 5 to n = 4
4. n = 6 to n = 5

The frequency of radiation emitted when the electron falls from n = 4 to n = 1 in a hydrogen atom will be:
(Given ionization energy of H = 2.18 × 10^–18 J atom ^–1 and h = 6.625 × 10^–34 Js):

1. 1.03 × 10¹⁵ s^–1

2. 3.08 × 10¹⁵ s^–1

3. 2.00 × 10¹⁵ s^–1

4. 1.54 × 10¹⁵ s^–1