Match the words with the definitions.

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Nuclear [ ]

Average [ ]

Molecule [ ]

To expand [ ]

1. To increase in size, number, or importance, or to make something increase in this way.

2. Being or using the power produced when the nucleus of an atom is divided or joined to another nucleus.

3. Typical and usual.

4. The simplest unit of a chemical substance, usually a group of two or more atoms.