How do you explain this question? - Atomic m vs average atomic m?

the atomic m unit is the same m as a proton/electron pair or a neutron. Because of this, the atomic m of any particular atom is always a whole number. The average atomic m gives a weighted average of all isotopes of a particular element and their relative scarcity. A mole of potassium is likely to be 39,1 grams because it contains all the isotopes. But no single atom can have a mass in amu that is not a whole number.