For the KCET exam, students choosing PCM (Physics, Chemistry, Mathematics) will face a different set of questions compared to those opting for PCMB (Physics, Chemistry, Mathematics, Biology). This is because PCMB students have an extra subject, Biology, which PCM students do not. The Karnataka Examination Authority (KEA) organizes separate exams for each of these four subjects.

The KCET exam usually takes place over two days. On the first day, you'll typically have the Mathematics and Biology exams held in different sessions. The second day is generally for the Physics and Chemistry exams, again in separate sessions. So, PCMB students will appear for all four subject exams, while PCM students will only take the Physics, Chemistry, and Mathematics exams.

While the syllabus for Physics and Chemistry will be the same for both PCM and PCMB aspirants, PCMB students will also have a distinct syllabus and a separate question paper specifically for Biology. Therefore, the entire set of questions a PCMB student answers will include Biology, whereas a PCM student's will not. Essentially, if you're a PCMB candidate, you'll tackle questions in all four subjects, whereas if you're a PCM candidate, you'll only answer questions in Physics, Chemistry, and Mathematics. This ensures that the exam caters to the specific subject combinations chosen by the students.

I hope this helps.