The Government of India Act of 1919 clearly defined

1. The Government of India Act of 1919, also known as the Montagu-Chelmsford Reforms, introduced significant changes in the administrative structure of British India. 2. Its most important feature was the introduction of 'dyarchy' at the provincial level and the demarcation of subjects between the central and provincial governments. 3. The Act clearly separated the subjects of administration into 'Central' and 'Provincial'. Provincial subjects were further divided into 'Reserved' subjects (administered by the Governor with his executive council) and 'Transferred' subjects (administered by the Governor with ministers responsible to the provincial legislature). 4. This demarcation aimed to define the jurisdiction and responsibilities of the central and provincial governments more clearly than before. Hence, option (B) is the most accurate description. 5. Option (A) is incorrect; while the Act expanded legislative councils, it didn't establish a clear separation of power between the judiciary and the legislature in the modern sense. 6. Option (C) is incorrect; the Act primarily focused on the legislative and administrative structure concerning central-provincial relations, not specifically redefining the powers of the Secretary of State and the Viceroy relative to each other as its main goal.