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.
Answer:
c
Explanation:
when the river is affected by the acid rain many species go into extinction
Answer: The partial pressure of oxygen in the mixture is 321 mm Hg
Explanation:
According to Dalton's law, the total pressure is the sum of individual pressures.

Given :
= total pressure of gases = 752 mm Hg
= partial pressure of Helium = 234 mm Hg
= partial pressure of nitrogen = 197 mm Hg
= partial pressure of oxygen = ?
Putting in the values we get:


The partial pressure of oxygen in the mixture is 321 mm Hg
The change is called melting