All interactions between the atmosphere and hydrosphere involve?
a-soil and living things
b-water and living things
c-gasses or particles in the air
d-living things and gasses or particles in the air

Option C

Explanation:

The lithosphere of the earth consists of all its land mass, rocky materials and soil particles. Likewise hydrosphere includes all water bodies be it ocean, river, sea, lakes etc. Biosphere consists of all living things i.e flora, fauna, human beings etc. and atmosphere consists of air.  

Now for interaction between atmosphere and hydrosphere, air and water bodies must interact.  

Option A shown interaction between lithosphere and biosphere

Option B shows interaction between hydrosphere and biosphere

Option D shows interaction between biosphere and atmosphere

Hence, option C can be chosen as correct option

when it is at an intermediate population density