89 questions on this topic of d- and f-Block Elements (NEET 2027 syllabus). Here are 12; tap one to see its answer and explanation.
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Answer: (C) [Xe] 4f⁵ 6s²
Promethium (Z = 61) follows neodymium (Z = 60, [Xe] 4f⁴ 6s²). Its ground-state valence configuration is 4f⁵ 6s², as the 5d orbital remains vacant until gadolinium.
Answer: (A) Separation of individual lanthanoid elements from one another becomes extremely easy.
Because of lanthanoid contraction, the ionic radii of Ln³⁺ change very smoothly and minimally across the series, resulting in nearly identical chemical properties that make their separation from one another quite difficult, not easy.
Answer: (C) Attainment of completely empty (4f⁰), exactly half-filled (4f⁷), and completely filled (4f¹⁴) subshells in their tripositive ions.
La³⁺ has an empty 4f subshell ([Xe] 4f⁰), Gd³⁺ has a half-filled 4f subshell ([Xe] 4f⁷), and Lu³⁺ has a filled 4f subshell ([Xe] 4f¹⁴). The extra thermodynamic stability of these configurations is reflected in the lower combined ionisation enthalpies required to form these trivalent ions.
Answer: (C) Mo (4d) and W (5d)
Due to the intervention of the 14 lanthanoid elements filling the 4f subshell, the normal increase in atomic size from 4d to 5d transition series is cancelled out. Therefore, pairs like Zr/Hf, Nb/Ta, and Mo/W have almost identical atomic and ionic radii.
Answer: (A) Lu³⁺
Lutetium (Z = 71) has the electronic configuration [Xe] 4f¹⁴ 5d¹ 6s². The Lu³⁺ ion has the configuration [Xe] 4f¹⁴, which possesses completely paired electrons (0 unpaired electrons) and is therefore diamagnetic.
Answer: (A) (A) and (B) only
Statement (A) is correct: 4f electrons have poor shielding. Statement (B) is correct: La³⁺ (empty 4f⁰), Gd³⁺ (half-filled 4f⁷), and Lu³⁺ (completely filled 4f¹⁴) gain extra stability, making ΔᵢH₃ abnormally low. Statement (C) is incorrect: Ta and Nb have almost identical radii due to the contraction. Statement (D) is incorrect: atomic/covalent radii exhibit irregular peaks (notably at Eu and Yb).
Answer: (B) Imperfect shielding of one 4f electron by another from the increasing nuclear charge
Lanthanoid contraction is attributed to the imperfect shielding of one electron by another in the same 4f subshell due to the diffused shape of f-orbitals. Consequently, as the nuclear charge increases by one unit at each successive element, the net attraction increases, pulling the electrons inward.
Answer: (A) Both Statement I and Statement II are correct.
Sm²⁺ has a 4f⁶ configuration and readily undergoes oxidation to the more stable Sm³⁺ (4f⁵) state, making it a good reducing agent. The +3 oxidation state is the predominant and most stable oxidation state across the entire lanthanoid series.
Answer: (A) Lu³⁺
Lutetium (Z = 71) in the +3 state has the electronic configuration [Xe] 4f¹⁴. With no unpaired electrons (n = 0), its spin-only magnetic moment is 0 BM.
Answer: (A) Both Statement I and Statement II are correct
Statement I is correct because the atomic radii of lanthanoid metals show pronounced irregularities (e.g., abnormally large radii in Eu and Yb), whereas Ln³⁺ ionic radii decrease steadily. Statement II is also correct because the metallic radius is determined by metallic bonding, where the participation of valence electrons and localized 4f configurations differ across the series.
Answer: (B) Dysprosium (Dy, Z = 66)
The electronic configuration of Dysprosium (Dy, Z = 66) is [Xe] 4f¹⁰ 6s², which has 5d⁰. Gadolinium has [Xe] 4f⁷ 5d¹ 6s², Lutetium has [Xe] 4f¹⁴ 5d¹ 6s², and Lanthanum has [Xe] 5d¹ 6s².
Answer: (A) Europium (Z = 63)
Europium has the configuration [Xe] 4f⁷ 6s². Removing two electrons gives Eu²⁺ with a stable half-filled [Xe] 4f⁷ configuration. Removing the third electron requires disrupting this half-filled 4f subshell, resulting in an exceptionally high third ionisation enthalpy.