Answer : 3. "Champaran Movement"
Explanation :

The Champaran Movement took place in 1917 in the Champaran district of Bihar, India. It was Mahatma Gandhi's first significant involvement in a mass movement in India. The movement was initiated to address the issues faced by indigo farmers who were forced to cultivate indigo and were subjected to oppressive policies by British indigo planters. Gandhi's involvement in the Champaran Movement marked the beginning of his strategy of nonviolent resistance and Satyagraha in the Indian independence movement.