La solution de bouillie bordelaise est elle un corps pur ou un melange

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

You are making a solution of calcium chloride dissolved in water. you add solid, stir, and it dissolves. you add just a spatula tip full, stir, and the solid does not dissolve. how could you describe the solutions before and after adding the spatula tip amount

  the mississippians were considered to be  horticulturalists, which means they were