Which one among the following is not a mixture?

A mixture consists of two or more substances physically combined where components retain their individual properties [2]. Graphite is an allotrope of carbon, meaning it is a pure elemental solid consisting only of carbon atoms arranged in a crystalline lattice [3]. Pure substances, which include elements and compounds, are not mixtures [4]. In contrast, glass is an amorphous solid mixture primarily composed of silica and other oxides [3]. Brass is a homogeneous mixture (alloy) of copper and zinc [3]. Steel is also a mixture, specifically an alloy of iron and carbon, often containing other elements like nickel or chromium to enhance properties [5]. Since graphite is a pure element and the others are alloys or complex amorphous mixtures, graphite is the only substance listed that is not a mixture.

Sources

1. [2] 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 > Snapshots > p. 131
3. [4] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.5.1 Prevention of Corrosion > p. 54
4. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures > A step further > p. 118
5. [5] https://sist.sathyabama.ac.in/sist_coursematerial/uploads/SMEA1201.pdf