Final answer:
The sequences with the lowest first ionization energies are Al, Ba, Ag, and Ca from their respective pairs. This is because ionization energy generally decreases down a group and increases from left to right across a period.
Step-by-step explanation:
The element sequence from each pair that has the lowest first ionization energy is:
- Al for pair A (S and Al)
- Ba for pair B (Ra and Ba)
- Ag for pair C (Ag and N)
- Ca for pair D (Ca and Ge)
Ionization energy tends to decrease as you move down a group in the periodic table because the electrons are further from the nucleus and experience greater shielding. It also tends to be lower as you move from right to left across a period because of the fewer protons resulting in less nuclear charge.