Identify the error in this sentence: The hotel formally known as The Apple Tree Inn re-opened as The Orchard Inn.

The sentence "The hotel formally known as The Apple Tree Inn re-opened as The Orchard Inn" contains the term "formally," which is incorrect in this context. The intended word is "formerly," which refers to something that existed in the past. "Formally" pertains to adherence to rules or conventions, which does not fit the meaning of the sentence. This misuse constitutes a spelling error in the choice of vocabulary.

The correct identification of this error is essential for accurate communication; using "formerly" would clarify that the hotel had a previous name. In contrast, the other options do not apply here, as the sentence maintains subject/verb agreement, does not have fragments or run-ons, and does otherwise convey a complete thought without lacking grammatical structure.