What happens to the parties of water as the liquid actively boils?

Item AM062004: As water boils, the molecules become separated from each other. What happens as liquid water boils? The molecules are destroyed. The mass of the molecules decreases.

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.