Answer:
s atomic orbital
Explanation:
Lets us consider 4s, 4p, 4d and 4f. Here 4 is the energy level or the principal quantum number. For all the atomic orbital s, p, d and f the energy level is the same. But the energy level of each
Atomic orbital is different. s atomic orbital has the lowest energy followed by p, d and f.
Arranging the atomic orbitals in order of increasing energy:
s < p < d < f
