It is extremely important that alarms are raised when conditions fall below optimum.
the guy on the hockey team was the optimum player
The camera was in optimum condition even though it was forty years old.
In the sentence "The amount of feedback that students receive is not optimal", the word "optimal" is an adjective, more specifically a predicate adjective modifying the simple subject of the sentence, "amount". The word "optimum" does not occur in the sentence, although "optimal" could reasonably be called an adjective corresponding to the noun "optimum". In informal speech, "optimum" itself is often used as an adjective, but "optimal" is preferable for the adjective form.
I am not writing a sentence using that word.
Some believe the optimum summertime temperature is 72-degrees while others like 80-degrees or above.
I can give you a sentence using the word galaxy.
This is a sentence using the word aviator.
a sentence using the word endotracheal
This is a sentence using the word monomer. :P
I am saying a sentence using the word collagen.
this is a sentence using the word armchair.
For optimum results follow directions.