The correct option "1 and 3 only" is accurate because the Government of India Act, 1919 introduced diarchy in the executive government of the provinces, allowing for a division of responsibilities between elected Indian ministers and government-appointed officials. It also provided for devolution of legislative authority from the central government to the provinces, enhancing provincial autonomy. However, while the Act continued the separate communal electorate for Muslims, it was not a new feature unique to the 1919 Act, but rather a continuation from earlier legislation, thus making it less significant in the context of principal features introduced by the Act.