what are all of the chords?
c7, c#7, d7, d7, d#7, e7, e7, f7, f#7, g7, g7, g#7, a7, a7, a#7, b7, b7
which chords have a perfect fifth?
g, g#, a, a, a#, b, b, c, c#, d, d, d#, e, e, e# (f), f, f#
and of those, which is a c sharp?
f#7