How is a homogeneous mixture defined?

A homogeneous mixture is defined by having its components evenly distributed throughout the mixture, resulting in a uniform composition. This means that no matter where you sample the mixture, the proportions of its components remain constant. The components blend so that they are not visually distinguishable from one another, which is a key characteristic of homogeneous mixtures such as saltwater or air. The even distribution allows for a consistent appearance and properties throughout the entire mixture, making it difficult to separate the individual components based on visual inspection alone.

The other options suggest characteristics that are typical of different types of mixtures or materials. For example, the first describes a heterogeneous mixture where components can be easily distinguished. The third indicates varying particle sizes, which would imply a mixture that is not uniform (also characteristic of heterogeneous mixtures). The fourth implies that the components can separate over time, which is also indicative of a heterogeneous mixture where differences in the physical properties lead to separation. Thus, it is the even distribution and indistinct nature of the components that define a homogeneous mixture.