Final answer:
The formula of the compound from Al3+ and N3- is AlN, as they combine in a 1:1 ratio to form an electrically neutral compound.
Step-by-step explanation:
The formula of the compound formed from the ions Al3+ and N3- will be determined according to the ionic charges. Since the ions have charges that are equal in magnitude but opposite in sign, the lowest whole number ratio of ions that will result in an electrically neutral compound is 1:1. Therefore, one aluminum ion will pair with one nitrogen ion to create the compound. The formula will not show the charges, and no subscript is needed when the ratio is 1:1. So the formula for the compound made from aluminum and nitrogen ions is AlN.