The correct sequence of the following events is:
3. Champaran Satyagraha
4. Nagpur Satyagraha
1. Bardoli Satyagraha
2. Rajkot Satyagraha

Let's understand each event in detail:

1. Champaran Satyagraha:
Champaran Satyagraha was the first non-violent civil disobedience movement led by Mahatma Gandhi in India. It took place in the Champaran district of Bihar in 1917. The movement was initiated to address the grievances of the farmers who were forced to cultivate indigo by the British landlords. Mahatma Gandhi, along with his followers, organized protests and strikes, demanding the abolition of the oppressive indigo plantation system. The success of the Champaran Satyagraha marked the beginning of the non-cooperation movement in India.

2. Nagpur Satyagraha:
Nagpur Satyagraha was a significant event in the Indian freedom struggle. It occurred in 1923 in Nagpur, Maharashtra. The Satyagraha was led by Dr. B. R. Ambedkar, who fought for the rights of the untouchables or Dalits. The movement aimed to secure political representation and equal rights for the Dalits. Dr. Ambedkar organized mass rallies and protests, urging the government to address the social and economic discrimination faced by the Dalits. The Nagpur Satyagraha played a crucial role in raising awareness about the plight of the Dalits and led to significant reforms.

3. Bardoli Satyagraha:
Bardoli Satyagraha was a successful peasant movement that took place in Bardoli, Gujarat, in 1928. The movement was led by Sardar Vallabhbhai Patel, who advocated for the rights of the farmers against the excessive land tax imposed by the British colonial administration. The farmers in Bardoli refused to pay the increased tax and organized protests and strikes. Sardar Patel's leadership and negotiation skills played a vital role in resolving the issue peacefully. Eventually, the British authorities agreed to reduce the land tax, and the Bardoli Satyagraha became a symbol of successful non-violent resistance in India.

4. Rajkot Satyagraha:
Rajkot Satyagraha was a significant event that unfolded in Rajkot, Gujarat, in 1939. The movement was led by Mahatma Gandhi, who fought against the oppressive rule of the local prince, Thakore Sahib. The Satyagraha aimed to address various issues, including excessive taxation, corruption, and mismanagement by the princely state. Gandhi organized boycotts, protests, and non-cooperation campaigns to challenge the authority of the prince. The Rajkot Satyagraha highlighted the importance of self-governance and played a crucial role in shaping the principles of the Indian freedom struggle.

In conclusion, the correct sequence of events is Champaran Satyagraha, Nagpur Satyagraha, Bardoli Satyagraha, and Rajkot Satyagraha. Each event played a significant role in the Indian freedom struggle and contributed to the broader movement for independence.