Which statement about the physical change of liquid water boiling into steam is true?

a. the heat added represents an energy change.
b. the action cannot be reversed.
c. the steam cannot conserve mass.
d. the weight lost represents a mass change

Answer is: a. The heat added represents an energy change.

The same substance is present before and after the psysical change (chemical composition is not changed), just with different form (shape) or state of matter.

Liquid water molecule gain heat (energy) and move faster (higher kinetic energy).

The average kinetic energy of molecules depends on the temperature, steam has higher temperature.