* Aluminum (Al) is a metal and can be decomposed by electrolysis (using electricity to break it down).

* Octane (C8H18) is a hydrocarbon and can be decomposed by combustion (burning) or other chemical reactions.

* Silicon (Si) is a metalloid and can be decomposed by certain chemical reactions, though it's relatively stable.

* Xenon (Xe) is a noble gas. Noble gases are extremely unreactive due to their full outer electron shells. They do not readily form chemical bonds and are considered to be monatomic elements (existing as single atoms).

Therefore, xenon cannot be decomposed by typical chemical means.