Answer: (4)
- Air is a gas mixture that comprises the atmosphere of the Earth.
- These gases are colourless and odourless, so we can’t see them, but we can only sense them.
- The atmosphere is an ocean of these gases.
- It is made up of 78% nitrogen, 21% oxygen and 1% other gases and water vapour.
- From place to place, the moisture content varies.
- As compared to wetlands, arid regions have less moisture content.
