Which one of the following is regarded as a basic structural feature of a presidential form of government?

Introduction / Context:
Different democratic systems are often classified as parliamentary or presidential. The Indian system at the Union level is parliamentary, while the United States system is a classic example of the presidential model. Understanding the basic structural features of these systems is essential for comparative politics and constitutional law. This question asks you to identify a key basic feature of the presidential form of government from among several institutional characteristics.

Given Data / Assumptions:
- The question contrasts features like rigid constitution, single executive, supremacy of legislature, residuary powers of states and collective cabinet responsibility.
- We assume knowledge of standard textbook descriptions of the presidential system, especially as seen in the United States.
- In the presidential system, the President is both head of state and head of government and is elected independently of the legislature.
- The question uses the phrase basic feature, indicating a characteristic that clearly distinguishes presidential from parliamentary systems.

Concept / Approach:
In a presidential system, the executive branch is led by a single individual, the President, who is both head of state and head of government. This single executive is elected separately from the legislature, has a fixed tenure and is not collectively responsible to the legislature. Separation of powers between the executive, legislature and judiciary is another hallmark, but the central identifying feature at the institutional level is the single executive combining ceremonial and real executive powers. In contrast, parliamentary systems have a dual executive in which the head of state and head of government are separate offices, and the cabinet is collectively responsible to the legislature.

Step-by-Step Solution:
Step 1: Recall that in presidential systems such as that of the United States, the President is both head of state and head of government.Step 2: Recognise that this arrangement is a single executive as opposed to a dual executive.Step 3: Identify the option that specifically mentions a single executive combining head of state and head of government.Step 4: Compare this with other options which describe features more typical of federalism or parliamentary government.Step 5: Select option B as the correct answer.

Verification / Alternative check:
To verify, think about how the United States system works. The President signs bills into law, commands the armed forces, represents the nation in foreign affairs and heads the executive branch. There is no separate prime ministerial office. This clearly reflects the concept of a single executive. Parliamentary systems such as those in India or the United Kingdom, on the other hand, divide these roles between a head of state and a head of government, confirming that the presence of a single executive is a defining feature of presidential government.

Why Other Options Are Wrong:
A rigid constitution with a difficult amendment procedure (option A) is more closely associated with federal states and can exist in both parliamentary and presidential systems. Supremacy of the legislature over the executive (option C) is a hallmark of the parliamentary system, not the presidential one, where separation of powers limits legislative supremacy. Residuary powers vested in constituent states (option D) is a feature of certain federations and does not specifically define the presidential model. Collective responsibility of the cabinet to the legislature (option E) is a classic characteristic of parliamentary systems like India and the United Kingdom and is absent in a pure presidential system where the executive is not collectively responsible to the legislature.

Common Pitfalls:
Many examinees confuse features of federalism with features of presidentialism and mistakenly treat them as the same. Another common error is to select collective responsibility because it sounds like a democratic principle, forgetting that it defines parliamentary rather than presidential arrangements. Keeping separate mental lists of features associated with structure of the state (unitary versus federal) and features associated with form of government (parliamentary versus presidential) can help avoid such confusion.

Final Answer:
Single executive combining head of state and head of government is a basic structural feature of the presidential form of government.