The maximum number of electrons that can be accommodated in a shell is indicated by the formula:

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RRB ALP CBT I 31 Aug 2018 Shift 1 Official Paper
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  1. 2n
  2. 2n2
  3. 2n3
  4. 2n−2

Answer (Detailed Solution Below)

Option 2 : 2n2
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The correct answer is 2n2

Key Points

  • Shells are the orbitals or paths of different and definite energies in which the electrons revolve.
    • They are represented as K, L, M, and N from lower to upper energies, where the innermost shell is the lowest and the outermost shell is the highest in terms of energy.
  • Each orbital is associated with a fixed number of electrons i.e., the maximum number of electrons present in s, p, d, and f subshells are 2, 6, 10 and 14.
  • The maximum number of electrons in a shell is given by 2n2. Hence option 2 is correct.
    • That means n=1, 2, 3...for K, L, M, N....shell.

Additional Information

  • The outermost shell can have a maximum of 8 electrons whereas the penultimate shell cannot have more than 8 electrons until there are 2 electrons in the outermost orbit.
  • There must be 18 electrons in the penultimate shell and 2 electrons in the outermost shell for an atom to have more than 2 electrons.
  • For filling the orbit with 18 electrons, the inner orbital must be complete and the outermost and the penultimate orbit must have 2 and 8 electrons.
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