Among the given statements, statement (b) is not correct. Sounds with frequencies below 20 Hz are called infrasound. Infrasound is too low-pitched for humans to hear. Sounds with frequencies above 20,000 Hz are called ultrasound. Ultrasound is too high-pitched for humans to hear. The frequency of sound waves is measured in hertz (Hz), or the number of waves that pass a fixed point in a second. Human beings can normally hear sounds with a frequency between about 20 Hz and 20,000 Hz. All other statements given in the question are correct.