This textbook is written in one volume strictly to cover the whole semester-based undergraduate syllabi of Indian universities following the new syllabus for B.Sc. (minor) and B.Sc. ( generic) courses and also universities of neighbouring countries, maintaining the lucidity of expression and explanation. Dr. Hrishikesh Chatterjee retired as Associate Professor from the Department of Chemistry of Ramakrishna Mission Residential College, Narendrapur, Kolkata. He is widely respected by the students and in the teaching world of physical chemistry as a teacher and is well-known for his existing books on physical chemistry. He was awarded a doctoral degree by Jadavpur University, Kolkata. He published many research papers on "The Physicochemical aspects of Drug -DNA interaction" and "Kinetics of Oxidation of Diols by potassium bromate in acid medium?. The author has also written ?Understanding Physical Chemistry (vol - I and II) for 4-year honours course according to the present syllabus. The vol - II of the book will be published soon.