Introduction:
The Advocate General is a constitutional authority appointed in India to provide legal advice and assistance to the state government. The appointment of the Advocate General is governed by the Constitution of India.

Explanation:
The correct answer is option 'D' - Article 165 of the Constitution of India. Let's discuss in detail why this is the correct answer.

Article 165 of the Constitution of India:
- Article 165 of the Constitution of India deals with the appointment of the Advocate General for each state.
- According to this article, the Governor of the state appoints an Advocate General to represent the state government in legal matters.
- The Advocate General holds office during the pleasure of the Governor.

Role and Functions of the Advocate General:
- The Advocate General performs various important functions, such as:
- Providing legal advice to the state government on matters of law and constitution.
- Representing the state government in the High Court and other courts in the state.
- Defending the interests of the state government in legal proceedings.
- Assisting and advising the state government in drafting legal documents, bills, and ordinances.
- Performing any other legal duties assigned by the state government.
- The Advocate General acts as a legal advisor to the state government and plays a crucial role in ensuring the government's compliance with the law and constitution.

Appointment Process:
- The Advocate General is appointed by the Governor of the state.
- The Governor appoints a person who is qualified to be appointed as a Judge of the High Court.
- The Advocate General holds office during the pleasure of the Governor, which means the Governor can remove the Advocate General from office at any time.

Conclusion:
In conclusion, the Advocate General is appointed under Article 165 of the Constitution of India. This article outlines the appointment process and the role of the Advocate General in providing legal advice and representing the state government in legal matters. The Advocate General plays a crucial role in upholding the rule of law and ensuring the government's compliance with the constitution.