Spring factor or free constant K= ?

Hint : When a conventional spring without stiffness variability features, it compresses or its resting position, it exerts on opposing force F approximately proportional to its change in length y.

Complete Solution:-
The rate of spring constant of a spring is the change in the force it exerts; divide by the change in deflection \[{\text{K = }}\dfrac{{\text{F}}}{{\text{y}}}\]
Where F is the force exerted and y is the deflection.
SI unit is N/m. A tension or compression spring rate is expressed in a unit of force divided by distance.
A tension spring is a spring that works by twisting, when it is twisted about its Axis at an angle it produces a torque proportional to the angle. A tension spring rate is a unit of torque divided by an angle i.e Nm/ radian.
spring factor follows Hooke's law which states that force spring is proportional to its extension (F= -KX)

Additional information:-
A spring is an elastic object that stores mechanical energy. Spring is typically made of spring Steel. Spring is made from a variety of elastic material, the most common being spring Steel. Small springs can be wound from pre hardened stock, while larger one are made from annealed steel and hardened after. Some nonferrous metals are also used including titanium for parts requiring corrosion resistance and beryllium copper for spring carrying electrical current. Torsion spring is designed to operate with the tension load, so the spring stretches as the load is applied to it. Compression spring is designed to operate with the compression load, so the spring gets shorter as the load is applied to it.
Robert Hooke stated the law in 1676. It is the States force (F) needed to extend or compress a spring by some distance (x) scale linearly with respect to that distance that i.e F=KX, where k is constant factor of the spring & x is small compared to the total possible deformation of the spring. An elastic body or material for which this equation can be assumed is said to be linear elastic. Hook law is an accurate approximation for solid bodies as long as force and deformation are small enough. The modern theory of elasticity generalized Hooks law said that strain of an elastic object or material is proportional to the stress applied to it.

Note:-
Hooke's law is only a first order linear approximation to the real response of spring and other elastic bodies to applied force. It must eventually fail once the force exceeds some limit, since no material can be compressed beyond a certain minimum size for a stretched beyond a maximum size without some permanent deformation or change of state. Many materials will deviate from hooke's law. There are useful springs based on beam bending that can produce force that is very non-linearly with displacement. Hooke's law of elasticity states that extension of an elastic rod is linearly proportional to its tension, the force used to stretch it. Similarly the contraction is proportional to compression. For deformation beyond the elastic limit, atomic bonds get broken and rearranged & and spring may snap, buckle or permanently deform. For the super elastic materials the linear relationship between force and displacement is appropriate only in the lower strain region