Answer
The correct answer is (b)
$$1.2\times10^{-19}\text{ J}$$
Work Step by Step
In order to determine the energy we have to compute the area under the force-displacement curve.
The triangular section area is
$S=\dfrac{1}{2}ab,$
$a = 50 \text{ nm}$
$b = 5.0 \text{ pN}$
So
$S=\dfrac{1}{2}50 \text{ nm}\cdot 5.0 \text{ pN} \approx 1.2\times10^{-19}\text{ J}$
