Which one of the following substances is not a mixture?

A pure substance consists of only one type of particle and can be either an element or a compound. Tin is a chemical element (Sn), meaning it is a pure substance that cannot be broken down into simpler substances by chemical means. In contrast, a mixture consists of two or more substances mixed together that retain their individual properties. Seawater is a mixture of water, salts, and minerals [1][2]. Soil is a heterogeneous mixture containing various organic and inorganic components [1][2]. Air is a homogeneous mixture (solution) primarily composed of gases like nitrogen and oxygen [1][3]. Since tin is an element and not composed of multiple substances with variable compositions, it is not a mixture.

Sources

1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures > Snapshots > p. 131
2. [2] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures > Prepare some questions based on your learnings so far ... ..................................................................................... ..................................................................................... ..................................................................................... ..................................................................................... ..................................................................................... > p. 132
3. [3] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures > Snapshots > p. 130