It is a Chemical reaction taking place un a solution in which one or more of the products is insoluble in the solvent, and so forms solid particles that fall to the bottom of the reactor
It would be C. because the student is using different amounts of fertilizer in each container
I think it is because it's easier to "control". Like the books usually said that the nucleus is the control center of the nucleus, so if the nucleus located at the center or near center of the cell. So like easy contact, easy control, easy communication etc.
