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The electronic configuration of Einsteinium is: (Given atomic number of Einsteinium = 99)

Structure of Atom · Class 11 · JEE Main Previous Year Question

Question

The electronic configuration of Einsteinium is:

(Given atomic number of Einsteinium = 99)

Options
  1. a

    [Rn] 5f10 6d0 7s2[\text{Rn}]\,5f^{10}\,6d^0\,7s^2

  2. b

    [Rn] 5f13 6d0 7s2[\text{Rn}]\,5f^{13}\,6d^0\,7s^2

  3. c

    [Rn] 5f11 6d0 7s2[\text{Rn}]\,5f^{11}\,6d^0\,7s^2

    ✓
  4. d

    [Rn] 5f12 6d0 7s2[\text{Rn}]\,5f^{12}\,6d^0\,7s^2

Correct Answerc

[Rn] 5f11 6d0 7s2[\text{Rn}]\,5f^{11}\,6d^0\,7s^2

Detailed Solution

🧠 Heading to the Finish Line Einsteinium (Z=99Z=99) is an actinide. Filling the 5f5f subshell is the primary activity in this region of the periodic table.

🗺️ The Configuration Trail

  1. The Core: Radon (Z=86Z=86) is the preceding noble gas.
  2. The Outermost: The 7s7s subshell is filled next: [Rn]7s2[\text{Rn}] 7s^2 (Total = 88).
  3. The Remainder: We need 99−88=1199 - 88 = 11 more electrons.
  4. The Filling: These electrons enter the 5f5f subshell.
  5. Final Result: [Rn]5f117s2[\text{Rn}] 5f^{11} 7s^2.

⚡ The "Actinide Count" Shortcut Einsteinium is the 11th11^{\text{th}} element after Actinium's start point. Thus, it must have 1111 electrons in its 5f5f subshell. (Note: 6d06d^0 because ff filling is preferred here).

⚠️ Common Traps Don't get tempted by 6d6d participation. Most heavy actinides skip the 6d6d level entirely after the initial jump from Actinium.

Answer: (c)\boxed{\text{Answer: (c)}}

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