What sound intensity level, in decibels, corresponds to the reference intensity I0 = 10^-12 W/m^2, the threshold of human hearing?

1. At the reference intensity I0, the ratio I / I0 equals 1. 2. Since log10(1) = 0, the sound intensity level formula gives beta = 10 x 0 dB = 0 dB. 3. This is stated directly as the threshold of human hearing, matching option A. _Source: OpenStax Physics (CC BY 4.0), Ch 14 "Sound", section The Decibel Scale_