Step 1: Understanding the Term
The phrase "Guardian of the public purse" refers to the constitutional office that is responsible for auditing all receipts and expenditures of the government to ensure financial accountability and that public funds are spent legally and wisely.
Step 2: Analyzing the Roles of the Offices
(A) Union Public Service Commission (UPSC): This is the central recruiting agency for the civil services.
(B) Election Commission of India (ECI): This body is responsible for conducting free and fair elections.
(C) Supreme Court: This is the highest judicial body, often called the "Guardian of the Constitution" and the guarantor of fundamental rights.
(D) Comptroller and Auditor General (CAG): The CAG of India, established under Article 148, is the head of the Indian Audit and Accounts Department. The primary role of the CAG is to audit all accounts of the Union and State governments and public sector undertakings. By scrutinizing government spending and reporting to Parliament/State Legislatures, the CAG acts as the watchdog or "Guardian of the public purse."
Step 3: Final Answer
The office of the Comptroller and Auditor General (CAG) is known as the "Guardian of the public purse". Therefore, option (D) is the correct answer.