Answer: In the sentence "Education is enlightening," "enlightening" is a participle, not a gerund.
Explanation: A participle is a verb form that functions as an adjective, modifying a noun or pronoun. In this sentence, "enlightening" modifies the noun "Education." It describes the quality of education as being enlightening, or providing knowledge and understanding.
On the other hand, a gerund is a verb form that functions as a noun, usually ending in "-ing." For example, "Reading is my favorite hobby." In this sentence, "reading" is a gerund, as it functions as the subject of the sentence.
In the original sentence, "enlightening" is not functioning as a noun, but as an adjective modifying "Education," making it a participle.