The question asks us to identify which option is NOT a Central Paramilitary Force under the Ministry of Home Affairs.

Option 1: Central Industrial Security Force (CISF) is a Central Paramilitary Force under the Ministry of Home Affairs. It is responsible for providing security to various government-owned industries, airports, and other critical infrastructures.

Option 2: Central Reserve Police Force (CRPF) is also a Central Paramilitary Force under the Ministry of Home Affairs. It is the largest Central Armed Police Force in India and is primarily involved in counter-insurgency operations and maintaining law and order in various states.

Option 3: Ladakh Scouts is NOT a Central Paramilitary Force. It is a regiment of the Indian Army, primarily composed of soldiers from the region of Ladakh. They are responsible for guarding the strategic border areas of Ladakh.

Option 4: Border Security Force (BSF) is another Central Paramilitary Force under the Ministry of Home Affairs. It is responsible for guarding the borders of India with Pakistan and Bangladesh, and also plays a crucial role in combating smuggling and illegal activities.

Therefore, based on the options provided, the correct answer is option 3 - Ladakh Scouts.