The unit used to measure the intensity of sound is the decibel (dB). It is a logarithmic unit used to express the ratio of a physical quantity, such as power or intensity, relative to a specified or implied reference level. The decibel is commonly used in acoustics and audio technology.
- Option (A) "Particles per hundred" is incorrect as sound is not measured in terms of particles.
- Option (C) "Particles per thousand" is also incorrect for sound measurement.
- Option (D) "Nanometer" is incorrect as nanometers are used to measure length, not sound.
Thus, the correct answer is (B) Decibel.