The correct answer is 24 Joule. The potential difference across the two points is directly proportional to the work done per unit charge. ⇒ V = W/Q, where V is the potential difference, W is work done and Q is the charge. ⇒ W=Q * V ⇒ we have Q = 2 coulomb, V = 12 Volt, ⇒ W = 2 * 12 ⇒ W= 24 joule