Calculate the molar concentration of an aqueous solution of nh3 at 10.9%w (d = 950 g l-1).

Molar concentration has units of moles of solute per liter of solution. Given the percent by mass and the density of the solution, we ca easily convert the concentration into molarity as  follows:

10.9 g NH3 / 100 g solution ( 950 g / L ) ( 1 mol / 17.04 g ) = 6.08 mol NH3 / L solution 

It says in the text that millions or people had come from different parts of the country to go into Washington, D.C. to protest. So congregate means to gather around in a mass.

So the context clues would be “meet on the National Mall” “millions of people” “their voices heard”.

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