Decibel is the unit for A. Speed of light B. Radio wave frequency C. Intensity of sound D. Intensity of heat

The correct answer is C. Intensity of sound.

Decibel (dB) is a logarithmic unit that expresses the ratio of a physical quantity (such as sound pressure, power, voltage, etc.) to a reference value. It is often used to express the intensity of sound, which is the amount of energy per unit area that is carried by a sound wave. The intensity of sound is measured in decibels (dB), with 0 dB being the threshold of human hearing. A sound that is 10 dB louder than another sound is twice as intense, and a sound that is 20 dB louder is four times as intense.

The other options are incorrect because:

• Option A: Speed of light is measured in meters per second (m/s).
• Option B: Radio wave frequency is measured in hertz (Hz).
• Option D: Intensity of heat is measured in joules per second per square meter (J/s/m2).