Two molecules of sulphur trioxide are indicated by________.

Explanation

To indicate two molecules of sulfur trioxide, we can follow these steps:

1. **Understand the Chemical Formula**: The chemical formula for sulfur trioxide is \( \text{SO}_3 \). This indicates that each molecule consists of one sulfur atom and three oxygen atoms.

2. **Indicate the Number of Molecules**: When we want to indicate more than one molecule of a substance, we use a coefficient in front of the chemical formula.

3. **Write the Coefficient**: To represent two molecules of sulfur trioxide, we place the number '2' in front of the chemical formula.

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