NCERT has made all the Text books from class I to Class XII freely available in Internet.These are available for free Downloading.
NCERT text books are the basis for various entrance exams conducted by different states for Medical and Engineering courses. Also NCERT text books are basis for all UPSC based exams,
Here are the links for the Text books for class XII
Mathematics
Mathematics Text Book -Part 11
Physics
Chemistry
Biology
Economics
Sociology
Social Change and Development in India
Political Science