In spectral series of hydrogen, the series which does not come in infrared region is

Options

A. Pfund
B. Brackett
C. Paschen
D. Lyman

Explanation

To solve the question regarding which spectral series of hydrogen does not fall within the infrared region, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Spectral Series**: The spectral series of hydrogen consists of different series based on the transitions of electrons between energy levels. The main series are:
- Lyman series
- Balmer series
- Paschen series
- Brackett series
- Pfund series

2. **Identify the Regions**: Each series corresponds to a specific region of the electromagnetic spectrum:
- **Lyman series**: Transitions to the n=1 level (ultraviolet region)
- **Balmer series**: Transitions to the n=2 level (visible region)
- **Paschen series**: Transitions to the n=3 level (infrared region)
- **Brackett series**: Transitions to the n=4 level (infrared region)
- **Pfund series**: Transitions to the n=5 level (infrared region)

3. **Determine the Series Not in Infrared**: From the above information, we can see that:
- The Lyman series is in the ultraviolet region.
- The Balmer series is in the visible region.
- The Paschen, Brackett, and Pfund series are in the infrared region.

4. **Conclusion**: The series that does not fall within the infrared region is the **Lyman series**.

### Final Answer:
The spectral series of hydrogen that does not come in the infrared region is the **Lyman series**.