One end of a light spring of spring constnat k is fixed to a wall and the other end is tied to a block placed on a smooth horizontal surface.
In a displacement, the work done by the spring is $\frac{1}{2}{\mathrm{kx}}^2.$ The possible cases are
a) the spring was initially compressed by a distance x and was finally in its natural length
b) it was initially streched by a distance x and finally was in its natural length
c) it was initially in its natural length and finally in a compressed position
d) it was initially in its natural length and finally in a stretched position.