MHTCET 16 May 2024 Shift 1 Paper

Concept:An element with a completely filled $4f$ subshell must have $4f^{14}$ in its expected ground state electron configuration.Explanation:The $4f$ subshell contains seven orbitals, so a completely filled $4f$ subshell holds $14$ electrons.Ytterbium (Yb) has atomic number $Z = 70$.Its expected ground state configuration is $[Xe]\,4f^{14}\,6s^{2}$.This confirms that all seven $4f$ orbitals are fully occupied in Yb.Europium (Eu, $Z = 63$) has $[Xe]\,4f^{7}\,6s^{2}$, so its $4f$ subshell is only half-filled.Cadmium (Cd, $Z = 48$) has $[Kr]\,4d^{10}\,5s^{2}$, which does not involve the $4f$ subshell at all.Tungsten (W, $Z = 74$) has $[Xe]\,4f^{14}\,5d^{4}\,6s^{2}$, but Yb is the element that completes the filling of the $4f$ subshell in the lanthanide series.Therefore, among the given options, Yb has a completely filled $4f$ orbital at its expected ground state configuration.Answer:Option B: Yb (Ytterbium).