The correct answer is option 'B' - Prime Minister of India.

Explanation:

The Prime Minister of India is the functionary under the Indian Constitution who can be compared with the President of the United States. Below are the reasons why the correct answer is option 'B':

1. Executive authority:
- Similar to the President of the United States, the Prime Minister of India holds the highest executive authority in the country.
- The Prime Minister is the head of government and exercises executive powers in the administration of the country.
- Both the US President and the Indian Prime Minister are responsible for implementing and executing laws and policies.

2. Appointment and role:
- The President of the United States is elected by the citizens through an electoral college system.
- Similarly, the Prime Minister of India is appointed by the President of India, based on the majority support in the Lok Sabha (the lower house of Parliament).
- Both the US President and the Indian Prime Minister serve as the chief executive of their respective countries and have significant decision-making powers.

3. Cabinet formation:
- The US President appoints various cabinet members who are responsible for specific departments and ministries.
- Similarly, the Indian Prime Minister forms a council of ministers, known as the Cabinet, to assist in the governance of the country.
- Both the US President and the Indian Prime Minister rely on their respective cabinets to implement policies and carry out administrative functions.

4. Leadership role:
- The President of the United States is considered the leader of the nation and represents the country in international affairs.
- Likewise, the Prime Minister of India plays a crucial role in representing the nation at the international level and providing leadership in domestic matters.

Conclusion:
Considering the executive authority, appointment and role, cabinet formation, and leadership responsibilities, it is evident that the Prime Minister of India can be compared to the President of the United States. Therefore, option 'B' is the correct answer.