Two colorless solutions are mixed together. Bubbles form as the solution is stirred. Give two possible explanations for this result.

Bubbles are often an indication that a reaction is occurring.

One possible explanation is that the bubbles represent a gas that is being produced through the reaction, and released from the solution. For example, if hydrochloric acid and water were combined, the formation of hydrogen gas is a possibility, and this gas would form bubbles as it is produced. 

A second possibility is that the reaction is exothermic, and the heat being released is vaporizing molecules that would otherwise remain in the gas phase of the reaction. For example, retaining our example of hydrochloric acid in water, if this reaction is sufficiently exothermic then some of the water could be vaporized into steam, which would then be released as a gas. 

An easy way to test which of the two gases is being released would be to collect it and see if it's flammable; the hydrogen gas would burn, while the steam would not.