A matter can exist in three different forms: solid, liquid, or gas.

Solid is a state of matter in which particles are closely packed and held together by strong forces, giving it a definite shape and volume. Examples of solids include ice, wood, and metal.

Liquid is a state of matter in which particles are close together but can move freely, giving it a definite volume but no definite shape. Liquids take on the shape of their container. Examples of liquids include water, oil, and mercury.

Gas is a state of matter in which particles are widely spaced and move freely, giving it neither a definite shape nor a definite volume. Gases take on both the shape and volume of their container. Examples of gases include air, oxygen, and helium.

Other states of matter, such as plasma and Bose-Einstein condensates, also exist under specific conditions.

Penicillin was discovered by Alexander Fleming, a Scottish bacteriologist, in 1928. Penicillin was first used to treat soldiers during World War II, and its introduction revolutionized the treatment of bacterial infections, saving countless lives. Today, penicillin and its derivatives are still widely used to treat a variety of bacterial infections, making it one of the most important discoveries in medical history.