If a 10-volt battery is placed across a 2-ohm resistance, a current of 5 amperes will flow.

Remember Ohms law... with very simple math the answer will be clear.

I still don't understand

Google "Ohms law".. it gives you the very simple mathmatical formula that will give you any of the three parts... Resistance, current or voltage... you can figure out if its true of false in about 30 seconds that way. It also will give you the answer to your other question.