Option 1: Salt Satyagraha refers to the non-violent protest against the British salt tax led by Mahatma Gandhi. It was a major campaign during the Indian independence movement.

Option 2: Individual Satyagraha was a movement launched by Gandhi in 1940 to demand individual freedom of expression. It aimed to secure political rights for Indians without challenging British authority directly.

Option 3: Ryots Satyagraha, also known as peasant Satyagraha, was a movement led by Gandhi in the Champaran district of Bihar in 1917. It was a protest against the oppressive conditions faced by indigo farmers.

Option 4: Flag Satyagraha was a protest held at Nagpur in 1923. It involved the hoisting of the Indian national flag despite it being banned by the British authorities. This act of defiance was an essential symbol of the struggle for independence.

The correct answer is option 4. Alert - correct answer should be Flag Satyagraha at Nagpur in 1923.