Answer : The correct option is, Molecules are speeding up as boiling occurs.
Explanation :
There are three states of matter which are solid, liquid and gas.
In the given diagram,
Arrow 1 shows the boiling process in which the phase changes from the liquid state to gaseous state at constant temperature.
Arrow 2 shows the melting process in which the phase changes from the solid state to liquid state at constant temperature.
Arrow 3 shows the sublimation process in which the phase changes from the solid state to gaseous state at constant temperature.
Arrow 4 shows the condensation process in which the phase changes from the gaseous state to liquid state at constant temperature.
Arrow 5 shows the freezing process in which the phase changes from the liquid state to solid state at constant temperature.
Arrow 6 shows the deposition process in which the phase changes from the gaseous state to solid state at constant temperature.
Hence, the arrow 1 represents the molecules are speeding up as boiling occurs.