Which element has the lowest ionization energy? A partial periodic table. 18 columns are shown; all columns align at the bottom. The first column is 6 entries, headed 1 and 1 A. Entries are upper H, upper L i, upper N a, upper K, upper R b, and upper C s. The second column is 5 entries, headed 2 and 2 A. Entries are upper B e, upper M g, upper C a, upper S r, and upper B a. 7 columns of 3 entries each follow; all entries are blank. The next column is 3 entries also; the first entry is upper N i and the rest are blank. 2 more blank columns of three follow. Five further columns of five entries each follow. The first of these is headed 13 and 3 A; entries are upper B, upper A l, and three blank cells. Next column is labeled 14 and 4 A; entries are upper C, upper S i, upper G e, and two blank cells. Next column is labeled 15 and 5 A; entries are upper N, upper P, and upper A s, with 2 blank cells below. The next column is labeled 16 and 6 A; entries are upper O, upper S, and upper S e followed by 2 blank cells. The next column is labele
argon (Ar)
bromine (Br)
cesium (Cs)
nickel (Ni)

Cs

Explanation:

This question is formatted oddly, but I understand the gist of it. Essentially, even if the periodic table is cut off by one row and missing the lanthanides and actinides, basic rules of the table still apply.

Remember the general trend of ionization energy: the farther to the right and the farther up, the higher the ionization energy.

As an example, fluorine is the "t-rex" of the elements because it's so electronegative that it hoards electrons, and that means it's hard to take its electrons away, which gives it a high ionization energy.

Out of the given choices, cesium Cs has the lowest ionization energy because it's so far to the left and so low. You can just nab an electron and it won't even mind too much.

Why not the other answer choices? Bromine is a halogen (so it's on the far right of the table) and it's fairly high up, so its ionization energy is much too high. Argon is a noble gas, so it's so stable that it hates it when someone tries to take an electron away; it has a very high ionization energy. Nickel, likewise, is a transition metal, so it's not the answer either.