To obtain the detailed syllabus for the optional subjects in the BPSC mains exam, you can follow the steps below:

1. Visit the official website: Go to the official website of the Bihar Public Service Commission (BPSC) at https://www.bpsc.bih.nic.in/.

2. Navigate to the syllabus section: Look for the "Syllabus" or "Examination" tab on the homepage. Click on it to proceed.

3. Find the BPSC mains exam syllabus: Look for the syllabus related to the BPSC mains exam. It should be mentioned separately for each optional subject.

4. Locate the optional subject syllabus: Scroll through the list of subjects until you find the desired optional subject for which you want the syllabus.

5. Click on the subject: Click on the subject to access the detailed syllabus. It will be displayed in a PDF format.

6. Download the syllabus: Click on the download icon or link to save the syllabus PDF file to your device for future reference.

7. Review the syllabus: Open the downloaded PDF file and carefully go through the syllabus. It will provide you with a detailed outline of the topics and subtopics that will be covered in the BPSC mains exam for the specific optional subject.

Remember, the syllabus will vary depending on the optional subject you choose. Each subject will have its own set of topics and subtopics that you need to prepare for the exam.

By referring to the official website of BPSC, you can easily obtain the detailed syllabus for the optional subjects in the BPSC mains exam. Make sure to regularly check the website for any updates or changes in the syllabus, if any.