Backward is an adjective, it describes how you glance.

One is also an adjective as it describes how many glances there were.

If you just keep in mind….

Verbs are doing words

Nouns are naming words

Adjectives are describing words

That would make the word “backward” an adjective, because it describes the word “glance,” a noun. So does “one.”

All three words “one backward glance” are part of a prepositional phrase, because the word “for” is a preposition. This preposition “for” is relating back to the verb “turned” to show the rest of the words why the person turned.

Don’t worry! Prepositions are a little tricky. They take time! Just know that they usually are the activities or indicators of activities of a person in motion…”under, on, by,” and “over, in, for, with” are all examples of prepositions.

“I” is the main noun (or person, place or thing) in the sentence, and “turned” the main verb, or action.

I’ve given you parts of speech for each word in the sentence and tried to explain. I hope my little teaching is helpful and not too bad! ;-} Read the sentence slowly outloud as you begin to understand how people may answer this question, and I bet you’ll understand quickly.

but backward would be an adjective as it describes the noun. an adverb describes a verb and usually ends in -ly

so if the sentence was ‘i slowly turned for one backward glance’ then slowly would be an adverb because it describes the verb turned.