Concept:
• The early 20th century saw the rise of the "Extremist" (Garam Dal) faction in the Congress.
• This group was led by the famous "Lal-Bal-Pal" trio, with each representing a different regional power center of the nationalist movement.
Step 1: Identify the components of the "Lal-Bal-Pal" trio
- 'Lal' stands for Lala Lajpat Rai.
- 'Bal' stands for Bal Gangadhar Tilak.
- 'Pal' stands for Bipin Chandra Pal.
Step 2: Assign leaders to their regional strongholds
- Bipin Chandra Pal was the extremist voice from Bengal (as noted in the question).
- Bal Gangadhar Tilak was the prominent leader from Maharashtra (specifically Pune/Bombay).
- Lala Lajpat Rai was the preeminent leader from the Punjab region.
Step 3: Confirm the identity of Lala Lajpat Rai
Lala Lajpat Rai is famously known as 'Punjab Kesari' (The Lion of Punjab) due to his massive influence and protests in that region, particularly against the Simon Commission.
Therefore, the blank should be filled with "Punjab".