Select the INCORRECTLY spelt word.

The incorrectly spelled word is "explaination." The correct spelling is "explanation," which refers to the act of making something clear or understandable.

Explanation of the other options:

☀ Acquaintance: This word is spelled correctly. It refers to a person known to one, but not a close friend.

☀ Acquisition: This word is spelled correctly. It refers to the act of acquiring or obtaining something.

☀ Aggregate: This word is spelled correctly. It can refer to a whole formed by combining several elements or to the total amount or sum of something.