Supplementary and reference books can be extremely helpful for Class 12 Commerce students as they provide additional explanations, examples, and practice questions to reinforce their understanding of the concepts covered in their textbooks. Here are some recommended supplementary and reference books for Class 12 Commerce:

1. "Accountancy - Part I & II" by NCERT:
- This textbook is prescribed by the CBSE board and covers all the topics related to accountancy.
- It provides a strong foundation in the subject and is the primary book for studying accountancy.

2. "Business Studies - Part I & II" by NCERT:
- Similar to the accountancy textbook, this book is prescribed by the CBSE board and covers all the topics related to business studies.
- It provides a comprehensive understanding of various business-related concepts.

3. "Economics - Principles, Statistics, and Applications" by T.R. Jain and V.K. Ohri:
- This book is highly recommended for economics students as it covers the topics in a detailed and well-structured manner.
- It also includes practice questions, case studies, and numerical problems to enhance the students' analytical skills.

4. "Mathematics for Class XII" by R.D. Sharma:
- This book is widely used by Class 12 Commerce students for mathematics.
- It provides a vast range of exercises and problems to practice and improve mathematical skills.

5. "Legal Studies for Class XII" by S.K. Singhal and R.K. Singhal:
- This book is specifically designed for students studying legal studies as an elective subject.
- It covers various legal concepts, case studies, and recent developments in the field.

6. "Statistics for Economics" by T.R. Jain and V.K. Ohri:
- This book is recommended for students studying statistics as a part of their commerce curriculum.
- It provides a comprehensive understanding of statistical concepts and includes numerous examples and practice questions.

7. "Indian Economic Development" by NCERT:
- This book is prescribed by the CBSE board and covers the Indian economic development section of the economics syllabus.
- It provides a detailed analysis of the Indian economy and its various sectors.

Remember, while these supplementary and reference books are highly recommended, it is essential to refer to the prescribed textbooks and study materials provided by your school or board.