2 musical notes that have a frequency ratio of 2 : 1 are said to be separated by an octave. A musical note that is separated by an octave from middle C (256 Hz) has a frequency of ?

Dear Student ,
Two notes separated by an octave have a frequency ratio of 2:1 .If a note is one octave below 256 Hz , then it must have one half of the frequency .
So the musical note has a frequency of 256 /2 = 128 Hz .

Regards