Both sentences are grammatically correct and convey the same meaning, but they use slightly different vocabulary. In the first sentence, "science classes" refers to the specific classes or courses that focus on science. In the second sentence, "science lessons" refers more broadly to any lessons or teachings related to science, regardless of whether they are part of a formal class or not. So, both sentences are acceptable, but the choice of wording may depend on the context and personal preference of the speaker.

Neither sentence is clear without context. They aren’t natural either. By ‘science’ do you mean a subject in school or the field? I like science because I find it interesting. (‘because’ is ok, but you can also just say I like science and find it interesting. I like going to Science. It’s interesting. (You are talking about a class you take in school. But we don’t usually call it ‘Science’ but use a more specific name like Biology, Physics etc) By the way, ‘interesting’ has a positive connotation so you don’t really have to add that you like it. Other things you can say: My Biology classes are interesting. Biology is interesting. (Either the field or the class, depending on context) Chemistry was interesting today. (My lesson) I usually like Physics but today’s lesson/class was confusing. Etc

Both are excellent. At school you enroll in a class, for example a class in Chinese History. That class continues for a semester or maybe for a year. That class contains many lessons, perhaps as many as three per week or fifty in a semester. So "class" is a broader concept than "lesson". You might say that your History class meets three times a week, but you can't say that your History lesson meets three times a week. If you like your teacher, you will say that you like your History class. If you particularly like the lecture she gave on one specific day, you would say that you enjoyed that lesson. In #1, you are saying that the course is interesting. In #2, you are saying that the lectures are interesting.