I understand that you are preparing for the JEE (Joint Entrance Examination) and you are looking for sources of difficult questions to enhance your preparation. Here are some suggestions on how you can find challenging questions for your JEE preparation:

1. Previous Year Question Papers:
- Solve previous year question papers of JEE Main and JEE Advanced. These papers are easily available on various online platforms and can provide you with a good understanding of the exam pattern and the level of difficulty.

2. Reference Books:
- Consult renowned reference books specifically designed for JEE preparation. Some popular books include:
- Physics: Concepts of Physics by H.C. Verma, Problems in General Physics by I.E. Irodov
- Chemistry: Organic Chemistry by Morrison and Boyd, Numerical Chemistry by P. Bahadur
- Mathematics: Mathematics for Joint Entrance Examination JEE (Advanced) by G.Tiwani, IIT Mathematics for JEE by M.L. Khanna

3. Online Platforms:
- Utilize online platforms like EduRev that offer a wide range of study materials and practice questions. You can find topic-wise difficult questions, mock tests, and solutions to assess your preparation level.

4. Coaching Institute Materials:
- If you are enrolled in a coaching institute, make sure to make the most of the study materials they provide. Coaching materials are usually designed to cover all the necessary topics and often include challenging questions to help you prepare better.

5. Study Groups and Forums:
- Join online study groups or forums dedicated to JEE preparation. Engaging with other aspirants can help you exchange knowledge, share resources, and find challenging practice questions.

6. Online Mock Tests:
- Take online mock tests that simulate the actual JEE exam environment. These tests can be found on various websites and provide detailed analysis of your performance, highlighting areas that require improvement.

Remember, while solving difficult questions is essential for JEE preparation, it is equally important to have a strong foundation and conceptual clarity. Make sure to thoroughly understand the basic concepts before attempting challenging problems. Regular practice, consistent efforts, and a well-structured study plan will greatly contribute to your success in the JEE examination. Good luck with your preparation!

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