The correct option is D An orbital is characterized by three distinct quantum numbers n, l and m
An orbital is the space around the nucleus where the probability of finding an electron is the highest. Orbitals do not represent the trajectory of an electron.
Also, orbitals are not always spherical.
It is true that an orbital is a space around the nucleus where the probability of finding electrons is maximum. But, it is not necessary that all the electrons of an atom are found in one orbital.
An orbital is always characterized by three quantum numbers. Those are: Principal quantum number (n), Azimuthal quantum number (l) and Magnetic quantum number (m).