To understand that gases are readily compressible, and liquids are not.
Everything in this universe is made up of materials which scientists have termed as "Matter". Matter is defined as anything that has mass and occupies space. Everything we can see, hear, touch, taste, and smell is matter. It is made up of tiny particles that cannot be seen with the naked eye. Air and water, gold and silver, table and chair, milk, and oil etc., are all different kinds of matter, because all of them occupy space and have mass.
Based on physical properties, matter is classified as solids, liquids, and gases. Matter is classified into elements, compounds, and mixtures based on its chemical properties.
Solids have a definite shape, distinct boundaries, and fixed volumes, and thus have negligible compressibility. Solids tend to maintain their shape when subjected to outside force. Solids can be broken by force, but changing their shape is difficult, so they are rigid.
Liquids do not have a fixed shape, but they do have a fixed volume. They take up the shape of the container in which they are kept. Liquid’s flow and change shape, so they are not rigid but can be called fluid. Solids and liquids can diffuse into liquids. The atmospheric gases diffuse and dissolve in water. These gases, particularly oxygen and carbon dioxide, are vital for aquatic animal and plant survival. All living organisms require oxygen to survive. Because of the presence of dissolved oxygen in water, aquatic animals can breathe beneath the water. As a result, we can conclude that solids, liquids, and gases can all diffuse into liquids. Liquids diffuse faster than solids. This is because particles in the liquid state move freely and have more space between them than particles in the solid state.
Gases are highly compressible as compared to solids and liquids. Compressed gas is found in liquefied petroleum gas (LPG) cylinders used in homes for cooking or the oxygen supplied to hospitals in cylinders.
Compressed natural gas (CNG) is used as fuel these days in vehicles. Due to its high compressibility, large volumes of a gas can be compressed into a small cylinder and transported easily.
In the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container.
