Which of the following elements has the smallest ionization energy?

A. F
B. Be
C. B
D. Mg
E. C

To determine the element with the smallest ionization energy among the given options, we need to understand what ionization energy is. Ionization energy refers to the energy required to remove one electron from an atom in its gaseous state.

The general trend of ionization energy across periods of the periodic table is as follows: it generally increases from left to right and decreases from top to bottom.

Now, let's analyze each option:

A. F (Fluorine):
Fluorine is located in group 17 (Group 7A) on the periodic table. It is the rightmost option, so it has a higher ionization energy than the other elements mentioned.

B. Be (Beryllium):
Beryllium is located in group 2 (Group 2A) on the periodic table. It is at the leftmost of the given options, indicating it has a lower ionization energy compared to the elements in the same period.

C. B (Boron):
Boron is located in group 13 (Group 3A) on the periodic table. It is to the right of beryllium and to the left of carbon, so it generally has a higher ionization energy than beryllium but lower than fluorine.

D. Mg (Magnesium):
Magnesium is located in group 2 (Group 2A) on the periodic table. It is identical to beryllium in terms of group and period. Hence, it has a similar ionization energy to beryllium.

E. C (Carbon):
Carbon is located in group 14 (Group 4A) on the periodic table. It is to the right of boron and to the left of nitrogen. Carbon generally has a higher ionization energy than boron but lower than nitrogen.

Comparing the given options, we find that the element with the smallest ionization energy is B. Be (beryllium) since it is at the leftmost position. The correct answer is B.

It becomes easier to pull electrons away (that's what ionization energy is) from an atom as the electron is further from the nucleus. Therefore, the smallest ionization potential will be that of the largest atom.