Introduction:
JEE Main is a national level entrance exam conducted by the National Testing Agency (NTA) for admission into various undergraduate engineering programs in prestigious institutions across India. The exam is offered in both online (computer-based) and offline (pen and paper-based) modes.

Appearing for JEE Main in Both Online and Offline Modes:
It is important to note that candidates can only appear for the JEE Main exam in either online or offline mode, and not in both modes simultaneously. Here are the details of each mode:

Online Mode:
1. Computer-Based Test (CBT): The online mode of the JEE Main exam is conducted as a Computer-Based Test (CBT).
2. Registration Process: Candidates who wish to appear for the online mode need to select the option for the computer-based test during the registration process.
3. Examination Centers: The online mode is conducted in designated examination centers equipped with computer systems.
4. Questions and Answering: In the online mode, candidates will be provided with a computer screen where they can read the questions and choose their answers by clicking on the appropriate option.
5. Time Duration: The duration of the online exam is the same as the offline exam, i.e., 3 hours.

Offline Mode:
1. Pen and Paper-Based Test (PBT): The offline mode of the JEE Main exam is conducted as a Pen and Paper-Based Test (PBT).
2. Registration Process: Candidates who wish to appear for the offline mode need to select the option for the pen and paper-based test during the registration process.
3. Examination Centers: The offline mode is conducted in designated examination centers where candidates are provided with a question paper and an OMR sheet to mark their answers.
4. Questions and Answering: In the offline mode, candidates need to read the questions from the question paper and mark their answers on the OMR sheet using a pen or pencil.
5. Time Duration: The duration of the offline exam is 3 hours, similar to the online exam.

Choosing the Mode:
During the JEE Main application process, candidates are required to select their preferred mode of examination. They can choose either online or offline mode based on their comfort and convenience. It is important to carefully consider the advantages and disadvantages of each mode before making the selection.

Conclusion:
Candidates appearing for the JEE Main exam can choose either online or offline mode based on their preference. The online mode is conducted as a Computer-Based Test (CBT) in designated examination centers, while the offline mode is conducted as a Pen and Paper-Based Test (PBT). Candidates should carefully evaluate their comfort and convenience before selecting the mode of examination.