Matter is anything that has mass and occupies space. Everything around us is made of matter.

An element is a pure substance that cannot be broken down into simpler substances by chemical means.

Water (H2O) is a compound made of hydrogen and oxygen atoms in a 2:1 ratio.

A mixture is a combination of two or more substances where each retains its properties and does not react chemically.

A uniform mixture, also known as a homogenous mixture, has components that are evenly distributed and indistinguishable.

A non-uniform mixture, or heterogeneous mixture, consists of visibly different substances where each component can be seen.

Air is a uniform mixture of gases including nitrogen, oxygen, and carbon dioxide.

Lime water is a solution of calcium hydroxide in water used to test for carbon dioxide.

Lime water turns milky due to the formation of calcium carbonate, an insoluble white precipitate.

An alloy is a homogeneous mixture of two or more metals, which offers unique properties distinct from the individual metals.

Bronze is an alloy made from copper and tin, typically in a ratio of 4:1.

Nitrogen, making up about 78% of air, does not support combustion and acts as a diluent for oxygen.

AQI is a tool used to communicate how polluted the air currently is or how polluted it is forecast to become.

A pure substance has a uniform and definite composition and cannot be separated into other substances by physical means.

Adulteration is the illegal process of mixing inferior substances with a product to increase quantity or reduce cost.

Water changes from ice to liquid to vapor when heated and vice versa when cooled, showing the same particles remain.

Melting (ice to water) and evaporation (water to vapor) are common state changes of water.

Pollutants include particulate matter like dust and gases such as carbon monoxide and sulfur dioxide which can affect health.