The central idea is the same as the main idea. Most of the time, the main idea is mentioned in the Title. Without reading the essay, I do not know what the central/main idea is.
Yes! Common nouns = Nouns name people, places, and things. Every noun can further be classified as common or proper. A common noun names general items.
Go into the kitchen. What do you see? Refrigerator, magnet, stove, window, coffee maker, wallpaper, spatula, sink, plate—all of these things are common nouns.
Leave the house. Where can you go? Mall, restaurant, school, post office, backyard, beach, pet store, supermarket, gas station—all of these places are common nouns.
Go to the mall. Who do you see? Teenager, grandmother, salesclerk, police officer, toddler, manager, window dresser, janitor, shoplifter—all of these people are common nouns.
The important thing to remember is that common nouns are general names of everyday items.
