v.) Carbon-carbon double bonds do not freely rotate like carbon-carbon single bonds because
a.) The double bond is much stronger and thus more difficult to rotate.
b.) Overlap of the two 2p orbitals of the pi bond would be lost during rotation.
c.) The shorter bond length of the double bond makes it more difficult for the attached groups to pass each other.
d.) Overlap of the sp² orbitals of the carbon-carbon pi bond would be lost.