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The problem could just be asking to compare the ionization energies of two elements and state which is larger. The energy of a photon = ionization energy plus the kinetic energy so the value of the ionization energy could also be used here for a photoelectric effect problem.
A good way to remember what this is would be to relate its trends to the trends in atomic radius since the larger the atomic radius, the greater the ionization energy, so their trends line up since they are in direct relationship with one another.
Yes and for the periodic trends you can always determine the trend based on stuff you already know (for instance atomic radius). As atomic radius increases as you go down a group, the nuclear pull on the outer electrons is less and thus the ionization energy is lower. Moreover, as you go across a period, the atomic radius decreases and as you adding electrons to the same energy shell, and therefore the ionization energy increases.