Final answer:
The word 'vapour' corresponds to option a) fog, which is made up of tiny liquid water droplets in the air, resembling a mist or vapor.
Step-by-step explanation:
Among the options provided, the one that matches the word "vapour" (meaning mist) is a) fog. Fog consists of tiny water droplets suspended in the air, which can be considered a type of vapor. This is similar to condensation that occurs when water vapor in the air cools down to form liquid water, such as on the outside of a cold beverage glass or in the form of fog.
Other forms of vapor or processes are also related to phase changes of water or other substances from solid or liquid to gas, or vice versa, such as dry ice subliming directly to carbon dioxide gas, producing a vapor that is visible when it condenses in the form of tiny water droplets in the air.