The correct answer is option 'D' - June 12, 1857.

The revolt of 1857, also known as the Indian Rebellion of 1857 or the First War of Independence, was a significant event in Indian history. It marked a major uprising against British colonial rule in India. The revolt began in Meerut on May 10, 1857, and quickly spread to various parts of the country, including Bihar.

The revolt in Bihar specifically started on June 12, 1857. Bihar played a crucial role in the rebellion, with several notable incidents taking place in the region. The revolt in Bihar was characterized by the active participation of both Indian soldiers, known as sepoys, and civilians.

Here is a detailed explanation of the revolt of 1857 in Bihar:

1. Causes of the Revolt:
- The revolt of 1857 was a response to various grievances faced by Indians under British rule.
- The introduction of new laws and regulations, such as the Doctrine of Lapse and the annexation of princely states, led to discontent among the Indian population.
- The use of Indian soldiers in foreign wars and the introduction of the new Enfield rifle, which required soldiers to bite off the ends of greased cartridges, sparked religious concerns.

2. Spread of the Revolt to Bihar:
- The revolt in Bihar started on June 12, 1857, when Indian soldiers stationed in Danapur, near Patna, rebelled against their British officers.
- The sepoys mutinied and marched towards Arrah, where they were joined by local leaders and civilians.
- The rebellion spread to other areas of Bihar, including Jagdishpur, Ara, and Shahabad.

3. Significant Incidents in Bihar:
- Jagdishpur: Kunwar Singh, a prominent leader in Bihar, played a crucial role in organizing the rebellion. He declared himself the ruler of Jagdishpur and led a successful resistance against the British forces.
- Arrah: The siege of Arrah was a notable event during the revolt. The British residents of Arrah, including the magistrate and his family, were besieged by the rebels for several weeks before being rescued by British forces.
- Shahabad: The district of Shahabad witnessed fierce battles between the rebels and the British forces. The rebellion was eventually suppressed by the British, but not without significant resistance.

4. Role of Bihar in the Revolt:
- Bihar's participation in the revolt of 1857 demonstrated the widespread discontent among the Indian population.
- The rebellion in Bihar was not limited to the sepoys but also involved civilians who actively supported the cause.
- The revolt in Bihar showcased the determination and bravery of Indian leaders like Kunwar Singh, who fought against British rule.

In conclusion, the revolt of 1857 started in Bihar on June 12, 1857. Bihar played a significant role in the rebellion, with several key incidents taking place in the region. The revolt in Bihar was a response to the grievances faced by Indians under British colonial rule and demonstrated the widespread discontent among the Indian population.