The caffeine content of coffee varies greatly, depending on the beans, how they're roasted, and other factors, but the average for an 8-ounce cup is about 100 milligrams (mg).
No, 'cat' is a common noun, a word for any cat of any kind. A proper noun is the name of a person, a place, a thing, or a title; for example: Cat Deeley, host of TV series 'So You Think You Can Dance'.
A noun can be categorized as either a common noun or a proper noun. A common noun is the word used for a class of person, place, or thing (e.g., person, city, dog). A proper noun is the given name of a person, place or thing, i.e., its own name (e.g., Michael, New York, Rover).