Final answer:
The valence electrons in phosphorus are closer to the nucleus than those in aluminum due to phosphorus having a greater effective nuclear charge while maintaining the same level of electron shielding as aluminum.
Step-by-step explanation:
The valence electrons in an atom of phosphorus are closer to the nucleus than the valence electrons of aluminum because phosphorus atoms have a greater effective nuclear charge with the same shielding as aluminum. This means that the answer is B) P has a greater effective nuclear charge with the same shielding as Al. The effective nuclear charge is the net positive charge experienced by valence electrons, reflecting the balance between the positive charge of the nucleus and the negative charge of the electrons between the nucleus and the valence shell. The shielding effect, the ability of inner electrons to shield valence electrons from the nuclear charge, is approximately the same for both elements because aluminum and phosphorus are in the same period and thus have the same number of inner electron shells.