Why do quantum-mechanical orbitals have “fuzzy” boundaries?

Solution 18Q

Step 1:

In quantum mechanical models of atomic structure, the Bohr orbits are replaced by wave-like states called orbitals. Unlike the orbits in the Bohr and Rutherford models, orbitals are not circles. They are three-dimensional shapes. The orbital with lowest energy is simply a sphere that surrounds the nucleus, but at higher energies orbitals have complex shapes.

The orbitals are denoted as 1s, 2s, 2p, 3s, 3p, 3d , 4s, 4p, 4d, 4f, 5s and so on..