Explanation:

To understand why aluminum (Al) is not a donor atom, we need to have a basic understanding of donor atoms and their characteristics.

Donor Atoms:
Donor atoms are atoms that have an excess of electrons in their outermost energy level and can easily donate these electrons to form chemical bonds. This property allows them to act as electron donors in chemical reactions, especially in the formation of coordinate bonds.

Properties of Donor Atoms:
1. Donor atoms have one or more lone pairs of electrons.
2. They are usually found in groups 15, 16, and 17 of the periodic table.
3. Donor atoms typically have a high electronegativity, which means they have a strong attraction for electrons.
4. They can easily form coordinate covalent bonds by donating their lone pair of electrons to an electron-deficient atom or ion.

Analysis of Options:
a) Phosphorus (P): Phosphorus is a group 15 element and has the electronic configuration 1s2 2s2 2p6 3s2 3p3. It has three lone pairs of electrons and can readily donate these electrons to form coordinate bonds. Therefore, phosphorus is a donor atom.
b) Antimony (Sb): Antimony is also a group 15 element and has the electronic configuration 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3. It has three lone pairs of electrons and can act as a donor atom.
c) Arsenic (As): Arsenic belongs to group 15 and has the electronic configuration 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3. It has three lone pairs of electrons and can act as a donor atom.
d) Aluminum (Al): Aluminum belongs to group 13 and has the electronic configuration 1s2 2s2 2p6 3s2 3p1. It has only one lone pair of electrons, which is not easily accessible for donation. Therefore, aluminum is not a donor atom.

Conclusion:
Based on the analysis above, the correct answer is option D, Aluminum (Al), as it does not possess the characteristics of a donor atom.