A compound is two or more chemically combined elements. Fore example NaCl, CO2, H2O
Amount Remaining Years #half lives
100g 0 0
50 g 100 1
25g 200 2
The answer is true the answer has to be 20 words long so true true true true true true
Answer:

The air in the atmosphere consists of nitrogen, oxygen, which is the life-sustaining substance for animals and humans, carbon dioxide, water vapour and small amounts of other elements (argon, neon, etc.). Higher in the atmosphere air also contains ozone, helium and hydrogen.