Across
- 2. This gas is used in strobe lights.
- 5. This gas can be used to fill party balloons.
- 6. Nearly 1% of the earth's atmosphere is...
- 10. Most of the visible universe is made of...
- 11. This gas helps keep swimming pools clean.
Down
- 1. A radioactive gas.
- 3. About 21% of the earth's atmosphere is...
- 4. About 78% of the earth's atmosphere is...
- 7. This gas is widely used in luminous signs.
- 8. When combined with tin, this gas helps keep your teeth strong.
- 9. This gas is used to make yellow-green 'neon' signs.