JEE Main 2020 · 6 September · morning · Single correct · +4 / −1
The set that contains atomic numbers of only transition elements, is :
- (a) 21, 32, 53, 64
- (b) 9, 17, 34, 38
- (c) 37, 42, 50, 64
- (d) 21, 25, 42, 72
Answer and solution
Answer (d) 21, 25, 42, 72
Solution
Chemistry ma’am · 3 steps
Learn where each d-block row starts and stops, then check every number against those ranges.
- The d-block ranges. Transition elements fill the d subshell. Their atomic numbers are 21 to 30 (3d), 39 to 48 (4d), and 57 plus 72 to 80 (5d).
- Watch the gap. Numbers 58 to 71 are the lanthanides. They fill the 4f subshell, so they belong to the f-block and count as inner transition elements, not transition elements. That is why 64 (Gd) does not qualify.
Option Elements Not transition (a) 21, 32, 53, 64 Sc, Ge, I, Gd Ge (p), I (p), Gd (f) (b) 9, 17, 34, 38 F, Cl, Se, Sr all four (p and s) (c) 37, 42, 50, 64 Rb, Mo, Sn, Gd Rb (s), Sn (p), Gd (f) (d) 21, 25, 42, 72 Sc, Mn, Mo, Hf none - So. Only (d) has all four numbers in the d-block: Sc (3d), Mn (3d), Mo (4d) and Hf (5d). The answer is (d).
The idea to keep. Memorise the d-block ranges: 21 to 30, 39 to 48, then 57 and 72 to 80. Numbers 58 to 71 are lanthanides, the f-block, so they are inner transition elements.
Answer from the NTA final answer key. Solution by PrepWiser.