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'.
Possessive proper nouns are the capitalized names of specific persons, places, or things. We recommend following the same rules for apostrophe use on proper nouns as you would on common nouns. For example: If the name does not end in -s, add -'s.