Which of the following are pure substances ?
Milk, iron, water, mercury, wood , air , blood, ink.

Explanation

To determine which of the following are pure substances, we need to understand the definition of a pure substance. A pure substance is made up of only one type of particle, which can be either an element or a compound. Now, let's analyze each option:

1. **Milk**: Milk is a mixture of water, fats, proteins, and other substances. Therefore, it is not a pure substance.

2. **Iron**: Iron is a chemical element consisting of only iron atoms. Hence, it is a pure substance.

3. **Water**: Water (H₂O) is a compound made up of hydrogen and oxygen atoms in a fixed ratio. Thus, it is a pure substance.

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