Answer : Option A) Molecules are speeding up during boiling.
Explanation : As shown in the above image it is clearly observed that the molecules are been transformed from liquid to gaseous state. Which means that the intermolecular distance between the molecules is increasing as they are boiling and getting transformed into gaseous form. They are speeding up to form gas from liquid state and achieve stability as the heat is supplied in greater amount. Boiling of liquid is causing the liquid molecules to speed up and get transformed into gaseous molecules.