There is no standard answer to this question as Biology textbooks vary from country to country and even from school to school. However, on average, a Biology textbook for class 12th would have around 20-30 chapters.
Here is a list of common topics that are usually covered in a Biology textbook for class 12th:
-Basic concepts of biology
-The chemical basis of life
-The cell
-Genetics
-Evolution
-Plant physiology
-Animal physiology
-Ecology
-Biotechnology
-Applied biology
