Under which constitutional Act passed by the British Parliament was the system of diarchy first introduced in the provinces of British India?

Introduction / Context:
Before India became independent, the British Parliament passed several Acts that gradually changed the structure of governance. One important experiment was diarchy in the provinces, where some subjects were administered by elected Indian ministers and others by British officials. This question asks under which Act this system was first introduced, a standard topic in Indian constitutional and freedom struggle history.

Given Data / Assumptions:

The question is about diarchy at the provincial level in British India.

Options include four major Acts passed between 1909 and 1947.

We assume awareness that each Act introduced specific reforms such as separate electorates, provincial autonomy or independence.

Concept / Approach:
Diarchy means dual rule. In the provincial context, it referred to dividing subjects into reserved and transferred categories. Reserved subjects like law and order remained under the control of the Governor and his executive council, while transferred subjects like education and health were handed to ministers responsible to the provincial legislature. This arrangement was introduced by the Government of India Act of 1919, also known as the Montagu Chelmsford Reforms. Later, the Government of India Act 1935 replaced diarchy in the provinces with provincial autonomy and introduced diarchy at the centre, but the first introduction was through the 1919 Act.

Step-by-Step Solution:
Step 1: Recall that the Indian Councils Act 1909 (Morley Minto Reforms) introduced separate electorates for Muslims but did not introduce diarchy. Step 2: The Government of India Act 1919 aimed to give more responsible government to Indians, especially in the provinces. Step 3: Under the 1919 Act, subjects in provinces were divided into reserved and transferred lists, forming the diarchy system. Step 4: The Government of India Act 1935 further changed the structure, giving provincial autonomy and planning diarchy at the centre, but it was not the first to introduce diarchy. Step 5: The Indian Independence Act 1947 simply ended British rule and did not introduce diarchy.

Verification / Alternative check:
A quick verification method is to match Acts with key features: 1909 is separate electorates, 1919 is diarchy in provinces, 1935 is provincial autonomy and a proposed federation, and 1947 is independence. Remembering this simple mapping helps fix the 1919 Act as the origin of diarchy in provincial governance.

Why Other Options Are Wrong:
Indian Councils Act, 1909: This Act expanded legislative councils and introduced separate electorates but did not divide provincial subjects into reserved and transferred categories.
Government of India Act, 1935: This Act abolished diarchy in the provinces and aimed to introduce it at the centre, but it was not the first Act to introduce diarchy in India.
Indian Independence Act, 1947: This Act granted independence to India and Pakistan and ended British sovereignty. It did not create any diarchic arrangement.

Common Pitfalls:
Students often mix up the provisions of the 1919 and 1935 Acts because both deal with provincial governance. A good way to avoid confusion is to remember that 1919 introduced diarchy in the provinces, while 1935 removed diarchy from provinces and expanded autonomy. Creating a small chronological summary of Acts and their main reforms can significantly improve accuracy in these types of questions.

Final Answer:
The system of diarchy in the provinces of British India was first introduced by the Government of India Act, 1919.