* No new substances are formed: Cloud formation involves water vapor in the air condensing into tiny water droplets or ice crystals. The water molecules themselves don't change their chemical composition. They simply change their state from gas (water vapor) to liquid (water droplets) or solid (ice crystals).

* The change is reversible: Clouds can dissipate when the water droplets or ice crystals evaporate back into water vapor. This demonstrates the reversibility of the physical change.

* No chemical bonds are broken or formed: Cloud formation doesn't involve any chemical reactions where bonds between atoms are broken or formed. It's simply a change in the physical state of water.

In summary: Cloud formation is a physical change because it involves a change in the physical state of water without altering its chemical composition.