The author has not indicated the name of the board concerned so that specific answer can be provided.
As far as CBSE is concerned the general rules are that the head of the college may permit change of subject combination subject to the condition that the request is made before 31 October of the academic session concerned. However, after passing the class XI, change of subjects are not allowed. Also, a candidate cannot offer a subject in Class XII which he/she has not studied and passed in Class XI. The Chairman of the board has powers to relax the rules for allowing change of the subject combination.
The author should, therefore, discuss the subject matter with his school principle for further guidance.
Regarding, his desire to become a doctor, it may be noted that first of all the class 10+2 level has to be passed for the purpose followed by securing a very high rank in the NEET examination to be able to get admission in the MBBS course.
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