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 proper noun is the name of a person, place, thing, or a title; for example: Snoopy or GarfieldDog Island, Franklin, FL or Cat Springs, TXDog Valley Road, Truckee, CA or Cat Rock Road, Greenwich, CTDog Day Afternoon, 1975 movie with Al PacinoCat on a Hot Tin Roof by Tennessee Williams.