Is sand, a solid, liquid, or gas?

Hint: The matter has three types: Solid, liquid and gas. The solid substance has a fixed shape, size and the molecules are bound strongly inside a solid. The liquid does not have a fixed shape, it holds the shape of the container and the molecules here are loosely bound. The gaseous substance also does not have the shape and the molecules here are free to move.

Complete step-by-step solution:
The matter is usually divided into solids, liquids, and gases. The solid substance has a fixed shape and the molecules inside the solids are bound strongly. Whereas, The liquid does not have a fixed shape since the molecules inside the liquid are very loosely bound.
Sand flows in an hourglass. It holds the shape of its container like liquids. One grain of sand is of course a solid, but a lot of grains together are a granular material. The granular material has quite different properties. Sand is a solid that pours like a liquid and holds the shape of its container. But It is still a solid, as each grain of sand individually has a shape of its own and keeps that shape.

Note:Beyond their practical importance, Physicists show interest in granular materials because they are not in the usual form of matter with unusual properties which are not still fully understood. The properties of granular materials are based on some basic ideas: Gravity applies a downward force on individual particles. The Friction between the particles based on the size and nature of the particles and also on the medium between the particles. So much mechanical energy is lost to heat as the particles move.