How many bits must be "flipped" (i.e., changed from 0 to 1 or from 1 to 0) in order to capitalize a lowercase that’s represented in ASCII?

Only one ... the third bit of the byte, numerical 32.  Every lower-case letter  has a '1' in that place.  If that bit is changed to '0', then the code represents the upper-case form of the same letter.

1 bit must be flipped because:A=01000001a=01100001So to go from a to A you have to change the 3rd bit from 1 to a 0.