Final answer:
The atom with the greatest ionization energy is F (Fluorine).
Step-by-step explanation:
The atom with the greatest ionization energy is: B) F (Fluorine).
The ionization energy is the energy required to remove an electron from an atom or ion. It is generally higher for atoms with smaller atomic radii and higher effective nuclear charges.
Fluorine (F) has the highest ionization energy among the given options because it is a smaller atom with a higher effective nuclear charge compared to the other elements (Sr, Br, and Na).