Please, explain what is the appropriate word here.
But it was the class/subject/course of chemistry that really interested him. At the age of 15, he went to college to study it.
Please, explain what is the appropriate word here.
But it was the class/subject/course of chemistry that really interested him. At the age of 15, he went to college to study it.
In English, one can be "interested in chemistry", and not likely in "chemistry class" or "subject." One can "take a chemistry class", though. So, I suggest "But it was chemistry that really interested him."
The term "chemistry course" is usually used for high school or university or out of school chemistry lessons.
Subject, because it is the whole field of chemistry that interests him and not one (for example) particular class with a particular teacher. (Although depending the preceding sentence, it would probably be more common to simply say, "But it was chemistry that really interested him.")
Contrast with: "His chemistry class interested him more than his math class."