From the given values find the potential difference between the point A and point B?

answer will be 5volts. it is based on a fact that when two closed circuits are joined only by a single wire then no current flow through that wire. Now rest is simple just take the potential of point A to be zero and potentioal across the 1ohm resistor of the wire connecting the two circuits will be zero.

You can see in the figure that, two closed loops are formed in the figure so the current flows through the wire jining two circuit will be zero. This is because current will keep on flowing in the lop and does not flow in the joining wire. so, answer would be 5v.