Question:

4d, 5p, 5f and 6p orbitals are arranged in the order of decreasing energy. The correct option is:

Updated On: Apr 25, 2026
  • 5f > 6p > 5p > 4d
  • 6p > 5f > 5p > 4d
  • 6p > 5f > 4d > 5p
  • 5f > 6p > 4d > 5p
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The Correct Option is A

Solution and Explanation

To determine the order of orbitals by decreasing energy, we need to use the (n+l) rule, where "n" is the principal quantum number and "l" is the azimuthal quantum number for the orbital type (s, p, d, f correspond to l values of 0, 1, 2, 3, respectively). The rule states that the sum of n + l determines the energy order. If two orbitals have the same n + l value, the orbital with the lower n value has lower energy.

  1. Calculate n + l for each orbital:
    • 4d: n = 4, l = 2, so n + l = 6
    • 5p: n = 5, l = 1, so n + l = 6
    • 5f: n = 5, l = 3, so n + l = 8
    • 6p: n = 6, l = 1, so n + l = 7
  2. Compare n + l values:
    • 5f has the highest n + l value (8), so it is the highest in energy.
    • 6p is next with n + l = 7.
    • Both 5p and 4d have n + l = 6, but 5p has a higher n value than 4d, meaning 5p is higher in energy than 4d.

Thus, the order of orbitals from highest to lowest energy is: 5f > 6p > 5p > 4d.

The correct option is: 5f > 6p > 5p > 4d.

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