The correct option is B Temperature doesn't change while internal energy changes
During processes of melting of ice or freezing of water temperature does not change i.e. dT=0 but internal energy changes. As dU=f2nR dT is only valid for ideal gases, so in ideal case only dU=0 when dT=0.
In real gases there exist intermolecular forces of attraction which is the reason for change in U.