Answer is: A. f > d > p > s.
Aufbau principle is a scheme used to reproduce the electron configurations of the ground states of atoms by successively filling subshells (orbitals) with electrons in a specific order.
Filling subshells in the following order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f.
The azimuthal quantum number (l) determines its orbital angular momentum and describes the shape of the orbital.
s-orbitals (for example 1s, 2s) are spherically symmetric around the nucleus of the atom.
p-orbitals are dumb-bell shaped. l = 0,1...n-1, when l = 1, that is p subshell.
d-orbitals are butterfly shaped.
f-orbitals are similar to the d orbital, but cut in half (eight lobes instead of four).
