Across
- 2. the number of times that a light wave (or a sound wave or a radio wave) vibrate (moves up and down)
- 3. the gases around the world
- 6. the smallest unit of a substance, with two or more atoms
- 7. a chemical that combines two or more elements
Down
- 1. a single living plant, animal, virus, etc.
- 4. a series of actions that you take in order to achieve a result
- 5. the line where the sky and the land or sea seem to meet