No.
No, you cannot charge an 8 volt battery with a 6 volt charger. The voltage of the charger must match the voltage of the battery.
You do not charge a 7.2 volt battery with a 9.6 volt charger period unless you want to ruin the battery. You charge it with a 7.2 volt charger.
Not on any modern car with a 12 volt system.
No, the battery charger has to match the voltage of the battery it is to charge.
No, a 12 volt charger will overcharge a 8 volt battery and destroy it.
No.
With a 12 volt battery charger that is made to plug into a 220 volt circuit.
No, an automobile battery charger outputs 12 Volts. This is far too many volts to charge a 5 Volt battery. You would destroy the 5 Volt battery with this charger.
Charge it with a 12 volt battery charger.
Some have a switch for 6 or 12V - if not you will "cook" a 6 volt battery using a 12 Volt charger
If you are asking the question, can you charge a 6 volt battery with a 12 volt charger, the answer is no.
A 12 volt battery charger is designed to charge 12 volt batteries.The answer to the Related Question explains how any battery charger works.