Decide which of the following atomic numbers are the atomic numbers of the inner transition elements
(A) 59
(B) 95
(C) 102
(D) 74
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B) and (C) only
The inner transition elements are the f-block elements, in which the 4f or 5f orbitals are being filled. They form two series: the lanthanoids, Ce to Lu (Z = 58–71), and the actinoids, Th to Lr (Z = 90–103).
(A) 59 — Correct. Z = 59 is praseodymium, \( \mathrm{[Xe]\,4f^{3}\,6s^{2}} \), a lanthanoid.
(B) 95 — Correct. Z = 95 is americium, \( \mathrm{[Rn]\,5f^{7}\,7s^{2}} \), an actinoid.
(C) 102 — Correct. Z = 102 is nobelium, \( \mathrm{[Rn]\,5f^{14}\,7s^{2}} \), an actinoid.
(D) 74 — Incorrect. Z = 74 is tungsten, \( \mathrm{[Xe]\,4f^{14}\,5d^{4}\,6s^{2}} \). Its 4f subshell is already full and the 5d subshell is being filled, so it is a transition element of the 5d series.