I just made a cake and someone already starting eating it! Ten percent is absent! (Kind of a strange situation. For something like cake we would typically say "half" or a "quarter" and instead of absent would say "missing" or "gone")
"Is" is used when the thing in question is "singular". "Cake" and "type" are singular.
"Are" is used when the thing in question is "plural". "Students" and "ones" are plural.
If you say "I like chocolate" it can mean either chocolate as in chocolate candy or just the flavor of chocolate in general. Chocolate milk, cake, pudding, ice cream, etc.