You cannot use a 220v appliance to a 120v outlet.
Ummm yes ? If your talking about a wall outlet yes you can have 120v dc but not at an outlet
No you cannot plug a 100v into a 120v outlet, it will fry whatever the product you are plugging up.
You don't unless it shows a dual rating on the appliance.
In the US on an 120v 15a outlet it's the short slot
UK is 220v
Some appliances may work, but I imagine most would either blow a fuse or just burn out. Definately not advised unless you use a transformer. With the right transformer everything should work fine.
you get an adapter
Yes, assuming the wall outlet produces 120V 60 Hz at at least 4 watts.
110 Volt is the nominal standard used in homes. Appliances are rated at 120 volts as a safety measure, as the voltage can fluctuate between 110v and 115v. Appliances rated in this manner will require voltages higher than 120v in order to sustain damage. Might call it a safety net for appliances.
Yes, no problem at all.