What are four everyday items that rely on the behavior of gases to operate properly?

A stove needs gas to burn (I only have one off the top of my head, sorry :/)

1. and 2. question: in which equation? or i don't understand you, 3. a), 4. c), 5. c), 6. b), 7. d), 8. d) if small number is underlined(behind symbol) , b) if big number is underlined(in front of symbol)9. what is underlined there? 10. c)

High-energy and unstable.