Final answer:
The 2s orbital is closest to the nucleus in the chlorine (Cl) atom compared to Al, S, Si, and P, as Cl has the highest nuclear charge among them, which pulls the electrons closer to the nucleus.
Step-by-step explanation:
The question assesses which atom has the 2s orbital closest to the nucleus out of the given elements: Al, Cl, S, Si, and P. The 2s orbital is an energy level that can hold electrons just above the 1s orbital, which is the orbital closest to the nucleus.
As we move across the periodic table from left to right within a period, the atomic radius generally decreases because the number of protons in the nucleus increases, pulling the electrons closer. Among Al, Cl, S, Si, and P, chlorine (Cl) has the highest atomic number and, therefore, the greatest nuclear charge, which draws its 2s electrons closer to the nucleus compared to the other atoms listed. Thus, the 2s orbital is closest to the nucleus in a chlorine atom. This ties into the principle that as effective nuclear charge increases, the orbitals pull in closer to the nucleus due to the stronger attraction.