Which of the following is an example of a liquid?

Rainwater is an example of a liquid because it possesses the characteristics typical of liquids: it takes the shape of its container, has a definite volume but no fixed shape, and flows easily. Additionally, rainwater is composed primarily of water, which is known for being a quintessential liquid within the context of physical states of matter.

The other choices represent different physical states: air is a gas, sand is a solid, and glass, while often categorized as a solid, has unique properties and is considered an amorphous solid. Therefore, rainwater stands out as the only option that accurately meets the criteria of a liquid.