Which Constitutional Amendment provides that the total number of ministers, including the Prime Minister, in the Council of Ministers shall not exceed 15 percent of the total number of members of the Lok Sabha?

Introduction / Context:
To prevent excessively large ministries and promote efficient governance, the Constitution was amended to cap the size of the Council of Ministers at the Union and state levels. This cap is expressed as a percentage of the strength of the Lok Sabha or the state legislative assembly. This question asks which Constitutional Amendment introduced the limit of 15 percent for the Union Council of Ministers including the Prime Minister.

Given Data / Assumptions:
- The focus is on the cap on the number of ministers in the Council of Ministers at the Union level.
- The cap mentioned is 15 percent of the total number of members of the Lok Sabha.
- The options list the 90th, 91st, 92nd, 93rd, and 86th Constitutional Amendments.

Concept / Approach:
The 91st Constitutional Amendment Act, 2003 introduced important anti defection related provisions and also placed a ceiling on the size of the Council of Ministers. At the Union level, it fixed the maximum number of ministers, including the Prime Minister, at 15 percent of the total number of members of the Lok Sabha. Similar caps were applied to state councils of ministers. Other amendments listed in the options deal with different subjects such as reservations, cooperative societies, or education.

Step-by-Step Solution:
Step 1: Recall that there was concern about very large councils of ministers at both the Union and state levels, leading to demands for a Constitutional cap. Step 2: Remember that the 91st Constitutional Amendment Act, 2003 addressed this issue and also strengthened anti defection provisions. Step 3: Note that this amendment specified that the total number of ministers including the Prime Minister shall not exceed 15 percent of the Lok Sabha strength. Step 4: Recognise that other amendments such as the 86th focus on right to education, while the 90th, 92nd, and 93rd relate to other issues. Step 5: Therefore, identify the 91st Constitutional Amendment as the correct answer.

Verification / Alternative check:
Standard Indian Polity textbooks and summaries of Constitutional Amendments clearly state that the 91st Amendment Act introduced the cap on the size of the Council of Ministers and included the 15 percent rule. Brief notes on amendments often list this as one of the key features of the 91st Amendment, which confirms the answer.

Why Other Options Are Wrong:
90th Constitutional Amendment: Deals with specific issues such as reservation of seats and is not associated with the size of the Council of Ministers.
92nd Constitutional Amendment: Related to changes in the Eighth Schedule regarding languages, not ministerial strength.
93rd Constitutional Amendment: Concerns reservations in educational institutions and not the Council of Ministers cap.
86th Constitutional Amendment: Introduced Article 21A on the right to education, unrelated to the size of the Council of Ministers.

Common Pitfalls:
Learners often confuse numbers of amendments because many important changes took place in the early 2000s. Some may wrongly associate the ministerial cap with amendments dealing with local bodies or education. A focused revision of key amendments and their main themes is necessary to avoid this confusion.

Final Answer:
The cap that the total number of ministers in the Union Council of Ministers shall not exceed 15 percent of the Lok Sabha strength was introduced by the 91st Constitutional Amendment.