I think the answer is c but I’m not for sure
Matter is the correct word.
Answer: D) protons.
The other option that would make the most sense would be electrons, however the mass of an electron is so small that is basically negligible, so it's not included in the atomic mass.
The periodic trend for atomic radius which quantifies us about the size of the atom increases as you go up a group (column) and increases as you go from left to right. When you locate Cadmium (Cd) and Germanium (Ge) in the periodic table, you see that Ge is one row higher above Cd. Furthermore, it is located more to the right than Cd. Then, definitely, Ge is larger than Cd.