Introduction:
The Union Public Service Commission (UPSC) is one of the most prestigious and competitive exams in India. To prepare for UPSC, candidates often refer to NCERT books, which are considered as the foundation for the exam. However, the question arises whether it is necessary to read all chapters of NCERT books for UPSC.

Importance of NCERT books:
1. Comprehensive Coverage: NCERT books provide a comprehensive coverage of various subjects in a concise manner. They are designed to build a strong foundation of basic concepts and principles, which is essential for UPSC preparation.
2. Clarity of Concepts: NCERT books are known for their clarity of concepts. They explain complex topics in a simple and easy-to-understand manner, making it easier for aspirants to grasp the fundamental ideas.
3. Authentic Information: NCERT books are authored by experts in the respective fields and are published by the National Council of Educational Research and Training (NCERT). They provide authentic and reliable information, which is crucial for the UPSC exam.

Reading all chapters:
1. Strong Foundation: Reading all chapters of NCERT books helps in building a strong foundation of knowledge. UPSC requires a holistic understanding of various subjects, and skipping chapters may lead to gaps in knowledge, which can be detrimental during the exam.
2. Interconnectedness of Topics: UPSC questions often require an interdisciplinary approach. Skipping chapters may result in missing out on important connections between topics, which can affect the overall understanding of the subject matter.
3. Hidden Gems: Some chapters may seem less important or less relevant at first glance. However, they may contain hidden gems of knowledge that can be useful in answering unexpected or unconventional questions in the exam. Hence, reading all chapters ensures comprehensive preparation.

Selective reading:
1. Time Management: UPSC preparation requires effective time management. Aspirants may choose to prioritize certain chapters based on their relevance, weightage in the exam, or personal strengths and weaknesses. This approach allows for better utilization of time and resources.
2. Focus on Core Areas: Candidates with a strong background in certain subjects may choose to focus more on advanced topics or specific chapters that are directly related to the UPSC syllabus. This strategy helps in optimizing the study plan and targeting key areas of the exam.

Conclusion:
While it is not mandatory to read all chapters of NCERT books for UPSC, it is highly recommended to do so. Reading all chapters ensures a strong foundation, comprehensive understanding, and the ability to make connections across topics. However, selective reading can be adopted based on individual circumstances and priorities. Ultimately, the key is to strike a balance between coverage and depth of knowledge to excel in the UPSC exam.