The balmer series for the H-atom can be ob-served

Options

A. if we measure the frequencies of light emitted when an excited atom falls to the ground state
B. if we measure the frequencies of light emitted due to transitions between excited states and the first excited state
C. in any transition in a H-atom
D. as a sequence of frequencies with the higher frequencies getting closely packed

Explanation

To understand the Balmer series for the hydrogen atom, we can break down the process into several steps:

### Step-by-Step Solution:

1. **Understanding the Balmer Series**:
The Balmer series refers to the spectral lines of hydrogen that are visible to the human eye. These lines are produced when electrons transition from higher energy levels to the second energy level (n=2).

2. **Energy Level Transitions**:
In the hydrogen atom, electrons can occupy different energy levels, denoted by quantum numbers (n). For the Balmer series, the transitions occur from n=3, 4, 5, ... to n=2.

3. **Photon Emission**:
When an electron transitions from a higher energy level (n2) to a lower energy level (n1), it emits a photon. The energy of this photon corresponds to the difference in energy between the two levels.

4. **Bohr's Formula**:
According to Bohr's theory, the wavelength (λ) of the emitted photon can be calculated using the formula:
\[ \frac{1}{\lambda} = R \left( \frac{1}{n_1^2} - \frac{1}{n_2^2} \right) \]
where R is the Rydberg constant, \( n_1 \) is the lower energy level (2 for Balmer series), and \( n_2 \) is the higher energy level (3, 4, 5,...).

5. **Calculating Wavelengths**:
- For the first line of the Balmer series (transition from n=3 to n=2):
\[ \frac{1}{\lambda} = R \left( \frac{1}{2^2} - \frac{1}{3^2} \right) \]
- For the second line (transition from n=4 to n=2):
\[ \frac{1}{\lambda} = R \left( \frac{1}{2^2} - \frac{1}{4^2} \right) \]
- Continue this for higher transitions (n=5, 6, etc.).

6. **Visible Region**:
The wavelengths calculated for the Balmer series fall within the visible spectrum, which means they can be observed as colored lines in the hydrogen emission spectrum.

7. **Conclusion**:
The Balmer series can be observed when measuring the frequencies of light emitted during the transitions of electrons from higher energy levels to the second energy level in a hydrogen atom.