Answer:
a) Al2O3
Explanation:
Aluminum generally forms Al3+ ions.
Oxygen generally forms O2− ions.
So when the metal and the non-metal bond together they form a neutral compound, i.e. Al2O3
(i.e. 2×3−3×2=0).
The ionic bonding is so strong (due to charge magnitude) in this material that it is reasonably insoluble.
