Which of the following correctly compares periodic properties of two elements and provides an accura — Atomic Structure Chemistry Question

STEPS:

1. Understand the periodic trend for atomic radius across a period:
* Chlorine ($\text{Cl}$) and sulfur ($\text{S}$) are both in Period 3 of the periodic table.
* As you move from left to right across a period, the atomic number increases, meaning the number of protons in the nucleus (nuclear charge) increases. Sulfur has 16 protons, while chlorine has 17 protons.
* Because the valence electrons for both elements are being added to the same principal energy level ($n = 3$), the core electron shielding remains relatively constant.
2. Apply Coulomb's Law to determine the relative atomic sizes:
* Because chlorine has a larger nuclear charge (more protons) than sulfur, its nucleus exerts a stronger electrostatic pull on the valence electrons.
* This stronger nuclear attraction pulls the electron cloud closer to the nucleus, making the atomic radius of $\text{Cl}$ smaller than that of $\text{S}$. This confirms Option D is the correct statement and explanation.

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WHY_OTHERS_WRONG:

• Option A is incorrect: Although aluminum ($\text{Al}$) has a larger nuclear charge than boron ($\text{B}$), its valence electrons occupy a higher principal energy level ($n = 3$ for $\text{Al}$ vs. $n = 2$ for $\text{B}$). Because $\text{Al}$'s valence electrons are farther from the nucleus and experience more shielding from core electrons, the first ionization energy of $\text{Al}$ is *less* than that of $\text{B}$, not greater.
• Option B is incorrect: Fluorine ($\text{F}$) does have a higher first ionization energy than oxygen ($\text{O}$). However, electronegativity is a periodic property itself rather than the physical cause of ionization energy. Additionally, the explanation contains a factual error: $\text{F}$ has a higher electronegativity than $\text{O}$, not the other way around.
• Option C is incorrect: While the atomic radius of calcium ($\text{Ca}$) is indeed larger than that of magnesium ($\text{Mg}$), the explanation is reversed. $\text{Ca}$ has its valence electrons in the $n = 4$ shell, meaning they experience more shielding from three inner shells of electrons compared to the valence electrons of $\text{Mg}$ (in the $n = 3$ shell, shielded by only two inner shells).