Which is the appropriate unit of measurement for pitch? decibel mel joule watt

The mel scale is used when people deal with the perception of pitch. The mel scale is about the apprehend  spacing of the frequencies.

1kHz is used as an implication point and then the mel scale is derived from there only.

Mel unit uses the apprehend pitch difference in a linear way as compared to hertz, thus Mel unit is used as the appropriate unit measurement for pitch.

Therefore, option (B) is correct.

found in the nucleus

has mass of one amu