The minimum percentage required in Class 12 for eligibility in the JEE exam varies according to different categories and the specific requirements of each college or university. However, there are some general guidelines that can help provide an understanding of the eligibility criteria.

General Eligibility Criteria:
- In order to be eligible for the JEE exam, candidates must have passed their Class 12 examination or any equivalent qualifying examination.
- They should have studied Physics, Chemistry, and Mathematics as compulsory subjects in Class 12.

Minimum Percentage Requirement:
- Most institutions require candidates to have a minimum aggregate percentage in their Class 12 examination to be eligible for the JEE exam.
- The minimum percentage requirement can vary from institution to institution, and it may also vary based on the category the candidate belongs to (e.g., General, OBC, SC/ST, etc.).
- Generally, candidates from the General category need to secure a higher percentage compared to those from reserved categories.

Specific Institutions:
- Some institutions may have specific requirements regarding the minimum percentage in Class 12 for eligibility in the JEE exam.
- For example, the National Institutes of Technology (NITs) and some Indian Institutes of Information Technology (IIITs) require candidates to secure a minimum of 75% aggregate marks in Class 12 (or equivalent examination) for admission in their undergraduate programs.
- However, it is important to note that these percentages may change from year to year and can vary across different institutions.

Additional Factors:
- It is important to keep in mind that the minimum percentage requirement is just one of the eligibility criteria for the JEE exam. There are other factors such as age limits, number of attempts, and specific entrance exam requirements that need to be fulfilled as well.

Conclusion:
The minimum percentage required in Class 12 for eligibility in the JEE exam varies across different institutions and categories. It is advisable for candidates to check the specific requirements of the institutions they are interested in and stay updated with any changes in eligibility criteria. Achieving a good percentage in Class 12 not only helps in meeting the eligibility criteria but also plays a crucial role in securing admission in esteemed institutions.