Ionization energy increases from left to right in the row and from bottom to top in a column. Also as we get closer to the nucleus it would be harder to take electrons out. B (atomic #5) has 2 layers of electron 2 and 3 atom in each layer. P has 15 so it would be 2,8 and 5 respectively. Ca is 20 so 2,8,8,2 and Zn is 30 and it would be 2,18,8,2. For energy between second and third ionization we are looking at taking out the 3rd electron. B already has 3 electron in the first layer so its easy to take them all. P has 5 in the last layer so again easy. But when we look at Ca and Zn after the 2nd electron (in the last layer) we should change the layer go one layer inside. So this needs more energy. To pick between Zn and Ca (they are in the same row) I mentioned earlier that in one row as we go to the right ionization energy increases so the answer is Zn.
