(c) The atom shown in A is Ne, and the atom shown in A cannot exist in ionic compounds.
There are no atoms in ionic compounds. Atoms are the original state of matter, without gaining electrons or losing electrons. At this time, the constituent matter is elemental. If there is a situation in which the electron is lost, that is, the atom becomes an ion, and the substance also becomes a compound, in which there are no atoms.

(d) more likely to bind to Ca2+.
B has a negative charge in the upper right corner, and the positive and negative charges attract each other.

Tip: If you see uncertainty in the question, try replacing the vague description of the question directly with something you know. Put an answer directly on your scratch paper, and follow the answer back to the process (if you need the process), but remember not to write the single example you think of directly on the test paper, because the individual does not represent the whole. This is just a trick to speed things up.
For example, if you look at B, you can substitute OH-, and the answer will come out very quickly.
Good luck with your studies!