Learning of science is a basic need in modern progressive society. We are so much impressed and excited by scientific achievements that we like to adopt a scientific attitude in all our daily activities. The present series, science.com, offers a new and challenging set of texts which has grown out of a modern approach for learning and teaching of science. The series has been revised on the guidelines give for continuous and comprehensive Evaluation. CCE refers to a system of school-based evaluation of students that covers all aspects of students development. Important features which have been retained in this edition to facilitate learning are interesting introduction at beginning of each chapter. Multicoloured figures, diagrams and tables to enhance the effectiveness of text. a large number of activities at appropriate places in the text for students to perform. Test yourself questions, for sel-assessment by the students. Some important points are given under the heading points to remember at the end the chapter. most importantly we have adopted an informal and interactive style in written this book. It is hoped that these features will help students learn science with most zest and excel in the subject. Although sincere efforts have been put in to make the book as useful as possible and error free readers are requested to send their suggestions to improve it.