What is the moisture in air called?

Humidity

The correct answer is option 4. Humidity.

The moisture in air is called humidity.

Here's why the other options are not correct:

Atmosphere: While the atmosphere encompasses all the gases surrounding the Earth, including water vapor, it's not specific to moisture.

Respiration: Respiration is the process of living organisms taking in oxygen and releasing carbon dioxide. It's associated with the exchange of gases but not specifically with moisture in the air.

Water vapor: While this is the physical form of moisture in the air, "humidity" refers to the amount of water vapor present in relation to the air's capacity to hold it.