Aluminium oxide is not reduced by chemical reactions due to (a) its highly stable nature (b) its highly unstable nature (c) its amphoteric nature (d) its highly explosive nature.

Compounds are considered chemically stable when their atomic and molecular structures have low potential energy, making them less reactive. This stability is tied to the chemical bonds that hold the atoms together; stronger bonds create more stable compounds.

In the case of aluminium oxide, (Al2O3), it is formed when aluminium metal reacts vigorously with oxygen to form a compound that is energetically favorable. This means that aluminium oxide's constituent atoms are at a lower energy state when they are combined than they were separately. As a result, additional energy is required to break these stable bonds, making aluminium oxide resistant to chemical reduction.

From the perspective of a reactivity series, aluminium is a reactive metal. Yet, once it forms aluminium oxide, the stability of the compound is significantly enhanced. This is due to the fact that it has completed its octet and reached a energetically stable configuration. Such stability is key in understanding why aluminium oxide is not easily reduced.

Delving into the ionic nature of aluminium oxide, we discover that this compound features a lattice of alternating positive and negative ions. Ionic bonds are formed through the electrostatic force of attraction between ions of opposite charges, in this case, Al3+ and O2- ions.

Ionic bonds are generally strong because of the substantial electrostatic force that holds the oppositely charged ions together. In aluminium oxide, each aluminium ion is surrounded by six oxygen ions, and each oxygen ion is surrounded by four aluminium ions, creating a robust, octahedral coordination geometry that contributes to the rigidity and high melting point of aluminium oxide.

Such a solid lattice structure makes it challenging to break these bonds and chemically reduce the constituent ions to their elemental form. This characteristic structure of aluminium oxide cements its place as a material with considerable chemical stability, requiring intense conditions to disrupt its ionic bonds.

Aluminium oxide is termed amphoteric owing to its ability to react with both acids and bases. This property stems from the oxide ions (O2-) in the compound that can react with additional acid to form water and a corresponding aluminium salt. Similarly, the Al3+ ions can react with bases to yield a salt and water.

For example, when aluminium oxide reacts with hydrochloric acid, it forms aluminium chloride and water. Conversely, if it reacts with sodium hydroxide, sodium aluminate and water are produced.

However, the amphoteric nature of aluminium oxide is not the reason it is difficult to reduce. The resistance to reduction is due to its ionic bond strength and overall stability, not its ability to interact with both acids and bases. Understanding this distinction helps clarify why certain properties of compunds affect reactivity and reduction potential.