Which of the above is / are correct? Answer:
1, 2 & 3
Notes:
Madhvacharya is the chief proponent of the Dvaita school of Vedanta. Madhva called his philosophy Tattvavāda meaning "arguments from a realist viewpoint".
Adi Shankaracharya propounded the Doctrine of Advaita (Monism). Advaita is a philosophy that emphasises on the oneness of the ‘personal self’ with the Supreme God.
Ramanujacharya is the chief proponent of Vishishtadvaita subschool of Vedānta. It is a non-dualistic school of Vedanta philosophy. It is non-dualism of the qualified whole, in which Brahman alone exists, but is characterized by multiplicity. It can be described as qualified monism or qualified non-dualism or attributive monism.