Answer:
Elastic Force
Step-by-step explanation:
As we pull the spring from one of its end by some distance such that its length is stretched by some amount "x"
So here the restoring force on the spring is given as

so here we know
k = coefficient of elasticity
x = change in the length of spring
So here the restoring force on the spring will be Elastic force which always act opposite to the direction of displacement of the spring