JEE Main 2024 · 6 April · morning · Single correct · +4 / −1
The number of element from the following that do not belong to lanthanoids is Eu, Cm, Er, Tb, Yb and Lu
- (a) 3
- (b) 1
- (c) 4
- (d) 5
Answer and solution
Answer (b) 1
Solution
Chemistry ma’am · 3 steps
Check each atomic number: lanthanoids sit between 58 and 71, and only one symbol falls outside that range.
- Know the range. The lanthanoids are the 14 elements from cerium (Z = 58) to lutetium (Z = 71), where the 4f subshell fills. The actinoids, thorium (Z = 90) to lawrencium (Z = 103), fill the 5f subshell.
Element Atomic number Series Eu (europium) 63 lanthanoid Cm (curium) 96 actinoid Er (erbium) 68 lanthanoid Tb (terbium) 65 lanthanoid Yb (ytterbium) 70 lanthanoid Lu (lutetium) 71 lanthanoid - The odd one. Curium is element 96, named after Marie and Pierre Curie. It fills the 5f subshell, so it is an actinoid. Lutetium, with [Xe]4f¹⁴5d¹6s², is the last lanthanoid.
- So. Only one element, Cm, is not a lanthanoid. The answer is (b).
The idea to keep. Learn the lanthanoids in order from Ce to Lu, 58 to 71. Then any unfamiliar symbol can be placed by its atomic number. Elements named after scientists, such as Cm, Es, Fm, Md and No, are actinoids.
Answer from the NTA final answer key. Solution by PrepWiser.