Answer:
Oxygen
Step-by-step explanation:
Aluminium atom ionic representation is usually Al3+. Aluminium usually gives out three electron when it reacts with other elements to attain the octet rule.
The cation A3+ of aluminium, their is a loss of electron .
So when aluminium reacts with another atom it gives the atom 3 electrons.
X value is diatomic, that means it exist as a molecule, like X2. The substance is gaseous at normal temperature and pressure as stated from the question . The substance can only be oxygen as it is diatomic in nature and exist as a gas at normal temperature and pressure.
The anion of oxygen atom is represented as O2- . That means it requires two electron to attain the octet rule.
Al3+ + O2-
cross multiply the charge
Al2O3
The substance is surely oxygen.