In the sound power level equation:

The value of X, i.e., reference power level, is established as:

Correct option is B

The sound power level equation (LW) is used to measure sound levels relative to a reference power. In acoustics, the reference power level (X) is universally defined as ( 10-12 watts. This value corresponds to the threshold of hearing for the average human ear, making it a standard in the measurement of sound power levels.
The formula:

is based on comparing the actual sound power (W) to the reference sound power (X) in watts.
Thus, the correct reference power level is 10−12 watts, making option (b) the right answer.
Information Booster: 1. Sound power level (LW) quantifies the power of a sound source relative to the reference level.
2. The reference power level (10−12 watts) is chosen because it represents the faintest sound audible to the human ear.
3. The logarithmic scale compresses a wide range of sound power values into a manageable range of sound levels (measured in decibels, dB).
4. Typical sound power levels include 0 dB (threshold of hearing) to 120 dB (threshold of pain).
5. The equation emphasizes the ratio of the actual power to the reference power.
6. It is commonly used in environmental noise assessments and acoustic engineering.