What is the solubility of salt in water at room temperature

The answer for #3 is c but i don't know why

How do temperature and salinity affect deepwater currents? as temperatures and salinity levels of water increase, the water rises to the surface where it creates currents as it moves to colder regions. they create changes in wind direction, moving denser water in the same direction as the wind and causing the deepwater circulation patterns found in the ocean. they equalize the forces on undersea currents caused by the coriolis effect as they replace more dense water with less dense water. they create density differences that cause dense deepwater currents to flow toward the equator where they displace less dense, warmer water above them.

About 3% of the water on earth is freshest. only about 40% of that freshwater is available for human use. why is so much freshwater unavailable for human use?