Based on the quantum mechanical concepts of the shielding effect (screening effect) and effective nu — Atomic Structure Chemistry Question

💡 Solution & Explanation

Electrons in $s$ and $p$ orbitals shield the nuclear charge effectively, whereas $d$ and $f$ orbitals have diffused spatial distributions leading to poor shielding (Statement A). Poor shielding directly increases the $Z_{eff}$ felt by valence electrons (Statement B). The $2s$ orbital penetrates closer to the nucleus than $2p$, lowering its energy in multi-electron atoms (Statement C). However, in a single-electron species like the Hydrogen atom, energy depends ONLY on the principal quantum number $n$; thus, $2s$ and $2p$ are exactly degenerate (equal in energy), making Statement D false.