The <em><u>MESOSPHERE </u></em>is the coldest layer and the hottest layer is <u><em>THERMOSPHERE </em></u> is the hottest layer in the atmosphere.
If you are adding something to the water the concentration of water would drop, as it would start off as 100% water but then with the addition of another substance it would change that from 100% free to x% free, due to the water dissolving the substance.
This questions seems like its missing other parts