The authors feel delighted to bring out the Twenty first thoroughly revised edition of this book. The present edition is strictly according to the latest syllabus and question paper design issued by the C.B.S.E. for the academic session 2026 – 2027. The salient features of this edition are : 1. As per the latest question paper design, Competency Based Questions have been appended at the end of each chapter which include Multiple Choice Questions, Very Short Answer Questions, Assertion Reason Based Questions and Case Study Based Questions. 2. Higher Order Thinking Skill (HOTS) based examples and questions have been added at the end of each chapter. 3. Mind Map and Chapter Test of each chapter have been incorporated in this edition. 4. All the questions of latest CBSE Question Papers and the Latest Sample Paper (Basic and Standard) issued by CBSE have been included in this edition. 5. A separate NCERT CORNER is given at the end of each chapter which contains all the examples and exercises of the latest NCERT Text Book along with Hints and Answers. 6. All the questions of NCERT EXEMPLAR PROBLEMS have been incorporated in this edition.