Which word in the following sentence is a conjunction?
In 1994, Dan Manion set the current record for a deep dive on air at 509 feet, but reported feeling strong effects of narcosis at such a depth.

A “conjunction” is a word that joins together sentences, clauses, phrases, or words. The only conjunction in this sentence is the word, “but.” “For” can be a conjunction, but in this sentence it is used as a preposition. “On” and “at” are prepositions.