Hello,

From what I could conclude, you've passed your half yearly examination with barely passing marks in Chemistry and are planning to take a medical leave for the final examination with the question that if you will be promoted to the next class that is 12th. If that's the case, let me tell you that this totally depends on your school and if we look at majority schools, they conduct re-examination for students who have failed to give final examination due to proper reason and proof. You will have to give your class 11th exams no matter what except in really serious and valid reasons, where the principal of your school might take a decision otherwise.

Hope this helps,

Thank you