Aluminum reacts with element x to form a compound with the formula al2x3. element x exists as diatomic molecules, x2, in the gaseous state at normal temperature and pressure. element x must be

Oxygen

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.      

c.

explanation:

a 20-cm-long, cylindrical graphite (pure carbon) rod is inserted into an oxidizing atmosphere at 1145 k and 1.013 x 105 pa pressure. the oxidizing process is limited by the diffu- sion of oxygen counterflow to the carbon monoxide that is formed on the cylindrical surface.