Explanation:

Alipore Bomb Case: The Alipore Bomb Case, variously called Muraripukur conspiracy or the Manicktolla bomb conspiracy was the trial of a number of revolutionaries of the Anushilan Samiti in Calcutta under charges of "Waging war against the Government" of the British Raj. It was held at Alipore
Sessions Court, Calcutta, between May 1908 and May 1909. The trial followed in the wake of the attempt on the life of Magistrate Kingsford in Muzaffarpur by Bengali nationalists Khudiram Bose and Prafulla Chaki in April 1908.

Saunder's murder: Just when the Hindustan Socialist Republican Association (HSRA) revolutionaries had begun to move away from individual heroic action, the death of Sher-i-Punjab Lala Lajpat Rai due to lathi blows received during a lathi- charge on an anti-Simon Commission procession led them once again to take to individual assassination. Bhagat Singh, Azad and Rajguru shot dead Saunders, the police official responsible for the lathicharge in Lahore in December, 1928.

Punjab Naujawan Bharat Sabha: Bhagat Singh had moved away from a belief in violent and individual heroic action to Marxism in mid 1920s and believed that a popular broad-based movement alone could lead to a successful revolution. That is why Bhagat Singh helped establish the Punjab Naujawan Bharat Sabha (1926) as an open wing of revolutionaries to carry out political work among the youth, peasants and workers, and it was to open branches in villages.

Hindustan Republic Association: The Hindustan Republic Association (HRA) was founded in October 1924 in Kanpur by Ramprasad Bismil, Jogesh Chandra Chatterjee and Sachin Sanyal, with an aim to organise an armed revolution to overthrow the colonial government and establish in its place the Federal Republic of United States of India whose basic principle would be adult franchise. Later it was renamed as Hindustan Socialist Republic Association.