apathetic is the adjective.
His apathetic attitude annoys me!
the boy had a record of apathy in his school file.
There was not much turnout this election due to voter apathy.
Many Americans believe voter apathy is the reason why less people are voting these days.
Apathetic.
Mr. Morgan was hoping for a classroom of eager learners, but as he looked out at the students' faces that first day, what he mainly saw was apathy.
Yes the word apathy is a noun. It is an abstract noun.
"Is apathy similar to indifference, or is it more like ennui?" -- though somehow I don't see that impressing your instructor much.
by adjective in the sentence
In a sentence.
NO but in the sentence "Use of the word "in" as an adjective is IN these days" the IN is an adjective
An adjective describes a noun.
My failure to attend university did not reflect my ability but instead my apathy. The council's apathy concerning the crime wave was most disconcerting. Her initial ardor was mysteriously replaced with apathy.