The correct answer is option 1: Montague. Montague, also known as Edwin Montague, was the person responsible for introducing the conception of Dyarchy in the 1919 Act. Dyarchy refers to a system of government where power is divided into two separate entities or authorities. In the context of the 1919 Act, it referred to the division of powers between the British government and Indian ministers. Montague was the Secretary of State for India at the time and played a key role in formulating the reforms introduced in the 1919 Act. It is important to note that while Montague was responsible for introducing the idea of Dyarchy, other individuals like Tez Bahadur Sapru, Lionel Curtis, and Chelmsford also played significant roles in shaping the provisions of the Act, but they were not primarily responsible for introducing Dyarchy.