Final answer:
The atomic orbital with a spherical distribution of electron density is the s orbital (option a). This spherical shape is unique to the s orbital, which is symmetrical around the nucleus.
Step-by-step explanation:
The type of atomic orbital that has a spherical distribution of electron density is the s orbital. The s orbital is unique in its spherical shape and represents the region in space where there is a high probability of finding an electron. Considering the different types of orbitals: (a) s orbitals are spherically symmetrical, (b) p orbitals have a dum/bbell shape, (c) d orbitals are rosette in shape or a combination of "dum/bbell + torus," and (d) f orbitals have even more complex shapes.
Each type of orbital is associated with a certain angular momentum quantum number (l). The s orbitals correspond to l = 0, p orbitals to l = 1, d orbitals to l = 2, and f orbitals to l = 3. Within these, the s orbital is the simplest with its spherical symmetry around the nucleus.
To answer the student's question, the correct option is (a) s Orbital.