Explanation: The -OH bond absorbs IR and vibrates at a characteristic and many times distinctive wave number of 3500cm-1. The -C=O would vibrate at 1700cm-1 though not clearly because -C-O bond typically vibrates around this point
Normally you would wash it with soap and water so I'm going to say A. soap. If you just rinse your hands with water they may not get all the way clean.
Think about it. Considering ionisation energy is the energy required to remove a single electron from the valence shell of an element in the ground state, the less energy it takes, the easier it is to remove.