Option 1: Assam Rifles - The Assam Rifles is a paramilitary force of the Indian Army. While they are deployed in Northeast India, including some areas on the northern borders of India, their primary role is to maintain law and order and counter insurgency operations in the region. They do have a role in border management, but they are not specifically deployed for monitoring borders, stopping smuggling, and preventing illegal immigration.

Option 2: Border Security Force (BSF) - The BSF is the primary border guarding force in India. They are responsible for guarding the land borders of India, including the northern borders. Their main tasks include preventing illegal infiltration, smuggling, and any other unlawful activities across the borders. They are also responsible for maintaining peace and tranquility in the border areas. Therefore, the BSF is a correct answer for the question.

Option 3: Indo Tibet Border Police (ITBP) - The ITBP is a specialized border guarding force deployed along the Indo-Tibetan border, including the northern borders of India. Their main role is to maintain border security, prevent unauthorized entry, and counter any threats from across the border. They are also involved in various other duties, such as disaster management and national security. Therefore, the ITBP