Who championed the idea of 'Democratic Socialism' ?

Ram Manohar Lohia

The correct answer is option (4) - Ram Manohar Lohia

The Socialists differentiated themselves from both the Congress and the Communists by advocating democratic socialism.
They criticized Congress for favouring capitalists and landlords while neglecting workers and peasants.
The Socialists faced a dilemma when Congress declared its goal as a socialist pattern of society in 1955 (Avadi Resolution), making it difficult to present themselves as a distinct alternative.
Some Socialists, led by Rammanohar Lohia, distanced themselves from and criticized the Congress, while others, like Asoka Mehta, advocated limited cooperation with the Congress.
The Socialist Party experienced splits and reunions, leading to the formation of various socialist parties such as the Kisan Mazdoor Praja Party, Praja Socialist Party, and Samyukta Socialist Party