Which one of the following statements about a compound is NOT correct ?

A compound is defined as a pure substance composed of two or more elements chemically combined in a fixed proportion [1]. Unlike mixtures, which are considered impure substances because they consist of various types of particles or molecules mixed physically, a compound is a pure substance because it consists of the same type of particles throughout [3]. The properties of a compound are unique and differ significantly from its constituent elements; for example, water (a liquid) has different properties than the hydrogen and oxygen gases that form it [2]. Furthermore, because the atoms in a compound are held together by strong chemical bonds, they cannot be separated by physical methods like filtration or distillation; they can only be separated into their constituent elements through chemical or electrochemical reactions [2]. Therefore, statement 3 is incorrect as compounds are pure, not impure, substances.

Sources

1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures > Snapshots > p. 130
2. [3] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures > 8.2 What Are Pure Substances? > p. 121
3. [2] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures > 8.3.2 Compounds > p. 124