In paragraph 4 what word or pharse gives you a clue to what the word perpendicular means

An aqueous solution of calcium hydroxide is standardized by titration with a 0.120 m solution of hydrobromic acid. if 16.5 ml of base are required to neutralize 27.5 ml of the acid, what is the molarity of the calcium hydroxide solution?

Find the number of grams of hcl needed to react completely with .50 moles of magnesium.

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?