This chapter explains the basic concepts of sound and its properties as per the Class 9 ICSE Physics syllabus. Students learn how sound is produced, transmitted, and detected, along with concepts like vibration, frequency, amplitude, and speed of sound. The chapter also covers important applications and numerical problems related to sound waves.Key Topics:• Production and propagation of sound• Characteristics of sound waves• Frequency, amplitude, and pitch• Speed of sound• Reflection of sound• ICSE Physics experiments and numericals