The correct answer is option 2, which is 1919.

Dyarchy refers to a system of dual government, where power is divided between two authorities. In the context of the Government of India, dyarchy was introduced through the Government of India Act of 1919.

Under this act, certain areas of governance were divided into two categories - reserved subjects and transferred subjects. The reserved subjects remained under the control of the central government, while the transferred subjects were handed over to the provincial government.

The intention behind introducing dyarchy was to gradually increase the participation of Indians in the governance of their country. However, it was met with mixed reactions and criticisms, and ultimately, it was replaced by a different system with the Government of India Act of 1935.

Therefore, the introduction of dyarchy in the Government of India Act occurred in 1919, as stated in option 2.