What is common between the following pairs of substances
water and mercury

Explanation

**Step-by-Step Solution:**

1. **Identify the Substances**: The two substances we are comparing are water and mercury.

2. **Understand Water**:
- Water has the chemical formula H2O, which means it is composed of two hydrogen atoms and one oxygen atom.
- Water is a form of matter that exists in three states: solid, liquid, and gas. In this case, we are focusing on its liquid state.
- Water is essential for life and is commonly found in a liquid state at room temperature.
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