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

Copper, silver, aluminum, cobalt, chromium, mercury 

True, the standard unit for volume is liters which can be represented by either a lower case "l" or a capital "l"

The atomic nucleus made up from protons (yellow) and neutrons (blue) and held together by nuclear forces. nuclear forces (also known as nuclear interactions or strong forces) are the forces that act between two or more nucleons. they bind protons and neutrons (“nucleons”) into atomic

Rate law for this reaction israte of the reaction = k[a]²[b].second order in a  means concentration of a in power of two, and  first order in b means concentration of b in power of one.