Iscotopes are usually stbolized in the following way:
X represents the chemical symbol
A rep Z represents the atomic number.
A and B are most closely on the diagram because if you look at A and D is on another side of the diagram than A is. B is on the same side as A. According to “Present time” A B and D are at the top of a arrow but it seems B is a little further down from the arrow if you look closely. This doesn’t change the fact that it’s closer to A.
Idk if this is the information you need but the energy level gets higher the farther you move down the Periodic Table. Every element in a vertical line has the same energy level.