National Council of Educational Research and Training (NCERT) was established by the Government of India in 1961. It is a premier non-profit educational research organiization. To the benefit of teachers, educators and students, it publishes curriculam-based textbooks for all classes and makes them available online for free. The copyrights of those books rests with NCERT. All the links given below route you to the original NCERT website.

Mathematics

Download Class 12 Mathematics Part-1
Download Class 12 Mathematics Part-2
Download Class 12 Mathematics Exemplar Problems

Physics

Download Class 12 Physics Part-1
Download Class 12 Physics Part-2

Biology
Download Class 12 Biology

Chemistry

Download Class 12 Chemistry Part-1
Download Class 12 Chemistry Part-2

History
Download Class 12 History - Themes in Indian History-1
Download Class 12 History - Themes in Indian History-2
Download Class 12 History - Themes in Indian History-3

Geography

Download Class 12 Geography - Fundamentals of Human Geography
Download Class 12 Geography - India -People And Economy

Economics

Download Class 12 Economics - Introductory Microeconomics
Download Class 12 Economics - Introductory Microeconomics