During the Delhi Durbar celebrations, a bomb was hurled at Viceroy Lord Hardinge while he was making his state entry into Delhi. Who was the main brain behind this assassination attempt?

Introduction / Context:
This question concerns revolutionary activities during the Indian freedom struggle, specifically an attempt on the life of Viceroy Lord Hardinge. Knowing who planned such actions sheds light on the underground revolutionary networks that operated alongside the open, constitutional nationalist movement.

Given Data / Assumptions:

• The event is a bomb attack on Lord Hardinge during his state entry into Delhi.
• The question asks for the main brain behind the attempt.
• Options list Ras Behari Bose, Bhagat Singh, Sachindra Sanyal and Jatin Das.
• We assume familiarity with different phases of revolutionary activity in India.

Concept / Approach:
The bomb attack on Lord Hardinge took place on 23 December 1912, when he was making a ceremonial entry into Delhi as the new capital of British India. The bomb was physically thrown by Basanta Kumar Biswas, but the principal organiser and planner of the conspiracy was Ras Behari Bose, a key revolutionary figure associated with the Ghadar movement and various plots against British rule. Exam questions typically ask for the main brain or organiser, which clearly points to Ras Behari Bose.

Step-by-Step Solution:
Step 1: Place the event in time: 1912, which is earlier than the period of Bhagat Singh's activities.Step 2: Recall that the bomb was thrown at Lord Hardinge during a state procession in Delhi.Step 3: Historical accounts identify Ras Behari Bose as the central organiser behind this attempt.Step 4: Bhagat Singh and Jatin Das were associated with later revolutionary actions in the late 1920s and early 1930s.Step 5: Sachindra Sanyal was an important revolutionary but is not usually named as the chief planner of this specific attack.Step 6: Therefore, the main brain behind the attack was Ras Behari Bose.

Verification / Alternative check:
Modern Indian history textbooks and exam guides describe the Hardinge bombing as part of early revolutionary activity in North India. They mention Ras Behari Bose as the key figure who planned the attack, while Basanta Kumar Biswas carried it out. Other revolutionaries are listed as associates, but Bose is consistently highlighted as the principal organiser, confirming him as the correct answer.

Why Other Options Are Wrong:
Bhagat Singh: Active mainly in the late 1920s; associated with the Assembly bombing and Saunders case, not the 1912 Hardinge attack.Sachindra Sanyal: Involved in revolutionary activity, especially in the United Provinces, but not widely recognised as the main planner of the Hardinge bombing.Jatin Das: Known for his hunger strike in jail and association with Bhagat Singh's group, not for this earlier conspiracy.

Common Pitfalls:
Because Bhagat Singh and Jatin Das are very famous, some students mistakenly associate all bombing incidents with them. Another pitfall is not paying attention to the date of the event. To avoid confusion, remember the pairing: 1912 Hardinge bombing – planned by Ras Behari Bose – executed by Basanta Kumar Biswas.

Final Answer:
The main brain behind the bomb attack on Lord Hardinge during his state entry into Delhi was Ras Behari Bose.