Final answer:
d) Moderately loud. A 100 Hz tone at 50 dB would be judged as moderately loud.
Step-by-step explanation:
A 100 Hz tone would be considered to be moderately loud, based on the given information. The question states that a 100 Hz tone at 50 dB will be judged as 'moderately loud.' This means that the tone would not be louder than normal or almost inaudible, but it would be loud enough to be noticeable. To put it into perspective, the question also provides examples of common sounds at different dB levels: running fingers through your hair is at 10 dB, inside a quiet home is at 50 dB, and the take-off of a jet plane is at 100 dB.