I would say D, because you need to start with nothing to measure the different sizes as they start to grow. hope this helps!
I think because each element has its own number of protons and neutrons, giving it its own atomic number and mass (correct me if I’m wrong please)
Ice melts when heat energy causes the molecules to move faster, breaking the hydrogen bonds between molecules to form liquid water.
Ca, V, Cu, Kr
Remember a period is a the horizontal rows in the Periodic Table.