The correct option is B. Vibrational motion
Explanation:
When an element or a substance is given heat, the molecules present in the element or substance start to vibrate. These vibrations cause the molecule to move back and forth with a certain force. If continuous supply of heat is given then the molecules will move so vigorously that the element or substance would expand.
When the supply of heat is reduced, the vibrations in the molecules of an element or substance would reduce.