Which statement correctly describes a heterogeneous mixture?

The correct answer is: Its composition is not uniform throughout the mixture.

Explanation:

A mixture is formed when two or more substances are physically combined without undergoing a chemical reaction. Mixtures are broadly classified into two categories based on how their constituent particles are distributed:

1. Homogeneous Mixtures: These mixtures have a uniform composition and appearance throughout. The components are mixed thoroughly down to the particle level, meaning you cannot visually distinguish one component from another (for example, salt dissolved completely in water).

2. Heterogeneous Mixtures: The prefix "hetero-" means different. A heterogeneous mixture is one in which the composition is not uniform throughout. The individual components remain distinct and separate, often creating visible boundaries or phases (for example, a mixture of sand and water, or oil and water).

Analysis of Options:

- "Its particles are uniformly distributed at particle level": This describes a homogeneous mixture, not a heterogeneous one.
- "Its composition remains fixed and constant always": Pure substances (compounds or elements) have fixed compositions, whereas mixtures can vary in composition.
- "Its composition is not uniform throughout the mixture": Correct, as defined by the non-uniform distribution of its components.
- "Its components cannot be separated by physical methods": Components of mixtures (both homogeneous and heterogeneous) can generally be separated using physical methods such as filtration, decantation, or evaporation.