The correct answer is option 2: 1915. Mahatma Gandhi returned to India from South Africa in 1915. During his time in South Africa, Gandhi had fought for the rights of the Indian community and had become a prominent figure in the Indian nationalist movement. He gained valuable experience and developed his principles of nonviolent resistance, which would later become central to his philosophy of Satyagraha. Upon his return to India, Gandhi became an influential leader in the Indian independence movement and played a crucial role in the struggle against British colonial rule. He led various nonviolent protests and campaigns, such as the famous Salt March, to advocate for the rights and freedom of the Indian people.