Which of the following is a core feature of a federal form of government as understood in political science and in the Indian constitutional context?

Introduction / Context:
Federalism is a system of government in which power is divided between a central authority and constituent units such as States or provinces. India is often described as a federal country with a strong unitary bias. This question asks which of the listed features is a core attribute of a federal system in general and of the Indian federal structure in particular.

Given Data / Assumptions:
- The options include supremacy of Parliament, supremacy of Judiciary, division of powers between the federal and State Government, and single citizenship.
- The question focuses on the general concept of a federal government rather than on a unique feature of Indian federalism alone.
- It is assumed that the student knows basic characteristics of federal constitutions from examples such as the United States, Canada and India.

Concept / Approach:
A classic definition of federalism emphasises a written constitution, a division of powers between the central and regional governments, an independent judiciary and a bicameral legislature as common features. Among these, the division of powers between two levels of government is considered a defining feature. Other features such as single citizenship, or even the degree of parliamentary supremacy, can vary between federal systems. In India, power is distributed among the Union, State and Concurrent Lists in the Seventh Schedule, which illustrates this division of powers. The approach is therefore to identify the option that best captures this essential characteristic.

Step-by-Step Solution:
Step 1: Examine Option A, supremacy of Parliament. While parliamentary supremacy is characteristic of systems such as the United Kingdom, federal systems often have a written constitution that limits the powers of Parliament, so supremacy of Parliament is not a defining feature of federalism. Step 2: Examine Option B, supremacy of Judiciary. An independent judiciary is important in a federal system to interpret the constitution and settle disputes between levels of government, but absolute supremacy of the judiciary is not the core defining feature; it is more of a supporting institutional requirement. Step 3: Examine Option C, division of powers between federal and State Government. This exactly describes the basic structure of federalism, where legislative and administrative powers are divided between the central government and the constituent units. Step 4: Examine Option D, single citizenship. Single citizenship is a distinctive feature of the Indian system, as opposed to dual citizenship in some other federations, but having single or dual citizenship is not what fundamentally defines a system as federal. Step 5: Since division of powers between federal and State Governments is the defining characteristic, Option C is the correct answer.

Verification / Alternative check:
Federalism is described in standard political science texts and Indian Polity books as involving a distribution of powers between two levels of government, each acting directly on citizens within its own sphere. The Constitution of India operationalises this through the Union List, State List and Concurrent List. Other features, such as an independent judiciary and a written constitution, are important but do not alone distinguish federal from unitary systems. This reinforces the choice of division of powers as the core feature of federal government.

Why Other Options Are Wrong:
Option A (Supremacy of Parliament) is wrong because it is more typical of a unitary parliamentary system like that of the United Kingdom, where Parliament can theoretically make or unmake any law, rather than a federal system where the constitution limits parliamentary power.
Option B (Supremacy of Judiciary) is wrong because in most federal systems the judiciary is independent and powerful, but not supreme in the sense of dominating all other organs; it interprets the constitution but does not define federalism by itself.
Option D (Single citizenship) is wrong because, while India has single citizenship, other federations have dual citizenship, and the nature of citizenship alone does not determine whether a system is federal or not.

Common Pitfalls:
A common error is to focus on a striking feature of Indian federalism, such as single citizenship, and assume it is the defining feature of any federal system. Another pitfall is to confuse the need for an independent judiciary with the concept of judicial supremacy and to treat that as the key characteristic of federalism. Students should remember that the central idea of federalism is sharing and dividing powers between two levels of government, each with defined areas of competence under a written constitution.

Final Answer:
The core feature of a federal government is the division of powers between the federal and State Government.