| Answer | Crossword Clue |
|---|---|
| OXYGEN | About 21% of the atmosphere |
| OXYGEN | Roughly 21% of the atmosphere |
| ARGON | About 1% of the atmosphere |
| ARGON | About 1% of the Earth's atmosphere |
| ARGON | About 1 percent of the atmosphere |
| ARGON | About 1 percent of the Earth's atmosphere |
