Higher the sum of the Principal quantum number (n) and Azimuthal Quantum Number (l), higher the
energy of the orbital.
Energy of orbital is low for minimum (n+l). If, orbitals have same (n+1), then smaller the ‘n’, smaller
(n + l) values for, 4d = 4 + 2 = 6
5p = 5 + 1 = 6
5f = 5 + 3 = 8
6p = 6 + 1 = 7
4d and 5p has same (n + l) value. Among them 4d has low ‘n’ and so, has lower energy than 5p.
6p will have lower energy than f, due to lower (n + l) value.
Decreasing order of energy of the given orbitals is 5f > 6p > 5p > 4d
Correct choice is (1)