Who among the following was a prominent leader of the Congress Socialist Party?

1. The Congress Socialist Party (CSP) was formed within the Indian National Congress in 1934 by socialist-leaning members. 2. M. N. Roy was a pioneer of communism in India and later advocated Radical Humanism; he was not a primary leader of the CSP. 3. Ganesh Shankar Vidyarthi was a prominent journalist and Congress leader, known for his work with the newspaper 'Pratap', but not primarily associated with the leadership of the CSP. 4. Pattam Thanu Pillai was a leader from Travancore (Kerala), involved in state politics and later served as Chief Minister, but not a key all-India leader of the CSP. 5. Acharya Narendra Dev was a leading Marxist theoretician and one of the founders and key leaders of the Congress Socialist Party, along with Jayaprakash Narayan, Ram Manohar Lohia, and others. He presided over the founding conference of the CSP in 1934. 6. Therefore, Acharya Narendra Dev was a prominent leader of the CSP.