Answer:
1.76 g/mL
Explanation:
You need to find the volume. You can do this by subtracting the volume of the water and the rock by the volume of the water.
72.7 mL - 50 mL = 22.7 mL
Now that you have volume, divide the mass by the volume to find the density.
39.943 g/22.7 mL = 1.76 g/mL
You have not mention here about those elements but the general concept for this is the:
uneven distribution ------> polar
even distribution -------> non-polar
The answer for the first question would be water. It is the substance that is a compound since it is made up of different elements. For the second item, i think the best answer is phosphorus and nitrogen. They are the limiting nutrients. For the last item, the correct answer is reservoirs.
