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'.
Common. Common nouns are your run-of-the-mill, generic nouns. They name people, places, things or ideas that are not specific. woman, city, dog, shoe. Since these nouns are not naming anything specific, they do not need to start with a capital letter unless they begin a sentence. Psst! If you need a refresher on nouns, see the nouns page.