Changing subjects after Class 11 starts: rules and reality
Usually possible in the first weeks, hard after that.
The window
Most schools allow changes in the first month or so of Class 11, subject to seats and blocks. CBSE registers Class 11 subjects on the board portal, after which changes need school and sometimes board approval.
What to do
If a subject is clearly wrong for you, say so in the first two weeks with a specific alternative. Waiting until the first exam makes the change harder and the catch-up longer.
Between Class 11 and 12
Changing after Class 11 means repeating a year of a new subject in Class 12 time. It is allowed in limited cases but is a last resort.
Guidance based on the CBSE scheme of studies and public exam bulletins. Confirm rules with your school and the official sources before deciding.