Final answer:
The spring constant of the spring is equal to the displacement (d) of the spring.
Step-by-step explanation:
The stretching of a spring is directly proportional to the force applied to it. This relationship is described by Hooke's law, which states that the force constant (k) of a spring is equal to the applied force (F) divided by the displacement (d) of the spring:
k = F / d
In the given scenario, the fish stretches the spring by an amount d when it is lowered to its equilibrium position. From this, we can conclude that the spring constant of the spring is equal to the displacement (d). Therefore, the correct answer is 1) The spring constant is equal to d.