Final answer:
The 'Chaali Mukte' were forty Sikh warriors who sacrificed their lives in battle after initially renouncing, then returning to fight for Guru Gobind Singh Ji, becoming known as the 'Forty Immortals'.
Step-by-step explanation:
The 'Chaali Mukte' referred to in the Sikh 'Ardas' were forty Sikh warriors who initially renounced Guru Gobind Singh Ji as their Guru but later recognized their mistake and fought bravely for him. They became martyrs on December 29, 1705, in a battle near the lake of Khidrana, also known as Isharsar, where they laid down their lives fighting for the Guru. Following their sacrifice, Guru Gobind Singh Ji blessed them as 'Chali Mukte', which means the Forty Immortals. In honor of their courage and sacrifice, the site of the battle was renamed Muktsar, translating to 'the Pool of Liberation'.