Correct option is (a) 1mW
Best explanation: Basically, the Decibel (dB) is a logarithmic unit which is used to state the gain of audio frequency amplifiers. This is so for the reason that the response of a human ear to the sound intensity exhibits logarithmic nature.
Apart from this, dBm is a unit which is often used in power measurement. dBm refers to the dB value which is estimated by assumption of a reference whose value is equal to 1mW.