Answer: The correct answer is Option D.
Explanation:
Mixture is defined as the combination of two or more different pure substances where each pure substance retains its original chemical properties.
A pure substances is defined as the substance that is formed by the combination of only one type of atom or only one type of molecule. The atoms or molecules forming a pure substance loose their original chemical properties.
From the given options:
Option A: carbon dioxide
Carbon dioxide is the combination of carbon and oxygen atom. This compound contains the molecules of carbon dioxide only. Thus, it is a pure substance.
Option B: silicon
Silicon element is formed by the combination of silicon atoms only. Thus, it is a pure substance.
Option C: Silicon dioxide
Silicon dioxide is the combination of silicon and oxygen atom. This compound contains the molecules of silicon dioxide only. Thus, it is a pure substance.
Option D: Sand
Sand is the mixture of silicon dioxide (known as quartz) with some rocks and minerals. Every substance retains its own chemical properties. Thus, it is a mixture.
From the above information, the correct answer is option D.
