The correct option is B 25 J
We know that, If the potential energy function U(x) is known, then the force at any position can be obtained by taking the derivative of the potential energy
⇒F=− dU dx
⇒−∫21F dx=∫21 dU
⇒U1−U2= Area under F−x curve
U1−U2=12×10×5=25 J
Hence option B is the correct answer