The series of hydrogen spectrum lying in infrared region is Paschen, Brackett and _____ series.

Explanation

To solve the question regarding the series of hydrogen spectrum lying in the infrared region, we will follow these steps:

### Step 1: Understand the Hydrogen Spectrum Series
The hydrogen spectrum consists of several series based on the transitions of electrons between energy levels. The main series are:
- Lyman series
- Balmer series
- Paschen series
- Brackett series
...