Which characteristic defines a homogeneous mixture?

A homogeneous mixture is characterized by a uniform composition throughout the entire mixture. This means that the individual components are so thoroughly mixed that they cannot be easily distinguished from one another. For instance, when salt is dissolved in water, the resulting saline solution is the same throughout, with salt ions evenly distributed in the water, making it impossible to see the individual grains of salt.

The uniformity in composition is what sets homogeneous mixtures apart from heterogeneous mixtures, where the components are easily distinguishable and not evenly distributed. While components in a homogeneous mixture can exist in different states, such as a solid dissolved in a liquid, the defining feature is the consistency of composition regardless of the states of the components. This clarity regarding uniformity of composition is essential for identifying and differentiating between various types of mixtures in chemistry.