The question requires us to choose between Ca and Ca cation which one would present the largest atomic radius.
To answer this question, we must keep in mind that a cation of an element is formed when this element loses an electron. Therefore, compared to the neutral atom X, a cation X+ would present one less electron, a cation X+2 would present 2 less electrons and so on.
Losing an electron (or more than one electron) means that the positive charge present in the nucleus of the atom - the protons - will become bigger than the negative charge present in the atom - the electrons. Since the amount of protons and electrons is not balanced the way it is in a neutral atom, the protons in a cation should exercise a stronger attraction over the remaining electrons compared to the neutral atom. As a consequence, the atomic radius of a cation is always smaller than the atomic radius of its correspondent neutral atom.
Therefore, considering Ca and its cation, the neutral atom Ca should present the largest atomic radius (the best option to answer is the second one, Ca).