Which of the following substances are elements?
Air, sodium, silicon, coal, tin, sugar

Explanation

To determine which of the given substances are elements, we need to understand the definition of an element. An element is a pure substance that consists of only one type of atom and cannot be broken down into simpler substances by chemical means. Let's analyze each substance provided in the question:

1. **Air**: Air is a mixture of different gases, including nitrogen, oxygen, carbon dioxide, and others. Since it contains multiple types of atoms, it is not an element.

2. **Sodium**: Sodium is a chemical element represented by the symbol 'Na' on the periodic table. It consists of only sodium atoms and cannot be broken down into simpler substances. Therefore, sodium is an element.

3. **Silicon**: Silicon is also a chemical element represented by the symbol 'Si'. It consists solely of silicon atoms and cannot be broken down further. Thus, silicon is an element.

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