Name the physical quantity which is measured in Decibel.
$(a)$ The speed of light
$(b)$ The intensity of heat
$(c)$ The intensity of sound
$(d)$ The frequency of radio waves

Hint – Decibel is the unit which is generally connected with sound, as we often say that humans have a hearing threshold of around 0 decibels.

Complete step-by-step answer:
Decibel – Decibel (dB) is the unit for expressing the ratio between two physical quantities, usually amounts of acoustic or electric power, or for measuring the relative loudness of sounds.
One decibel (0.1 bel) equals 10 times the common logarithm of the power ratio.
Thus we can say that the decibel is the unit of physical quantity used for the intensity of sound.
Hence option (C) is correct.

Note – The decibel (db) is a logarithmic unit used to measure sound level. It is widely used in electronic, signals and communication. The db is a logarithmic way of describing a ratio. The ratio may be power, sound pressure, voltage or intensity.