Explain where the water that collects on the outside of a cold drink on a hot day comes from.

It is because water molecules in the air condensed on to the container of the drink.

Explanation:

The way this works is the water molecules outside are hot and in the gas state, so when they come into contact with the cold side of the container they lose energy due to heat transfer between the molecules and the container, becoming a liquid on the side of the drink.