What kind of mixture is a solid, liquid, or gas that has a uniform composition?

A Homogenous Mixture is a solid, liquid, or gaseous mixture that has a uniform composition. No matter where you sample the mixture the amount and type of components is the same. It may be impossible to visually distinguish between a homogenous mixture and a pure substance.

However, you can tell them apart if you know their composition. There is more than one component in a homogeneous mixture, while a pure substance consists of a single element or compound. Iron is a pure substance, while steel is a homogeneous mixture. Oxygen gas (O2) is a pure substance, while air is a homogeneous mixture. Water (H2O) is a compound, but seawater is a homogeneous mixture.

A compound forms when elements and molecules chemically react with each other to make new products. Constituents of a homogeneous mixture do not react with each other and do not form new products. While the components of the mixture retain their chemical identity, they aren't visibly separate. But, at the molecular level, the mixture contains multiple compounds or elements.