For elongation of rod under its own weight
We know \(\Delta x=\frac{\rho g x^2}{2 Y}\) \(\left\{\begin{array}{l}\text { Where, } \\ \Delta x=\text { Elongation } \\ \rho=\text { Density of rod } \\ Y=\text { Young's modulus } \\ L=\text { Length } \\ g=\text { Acceleration due to gravity } \\ x=\text { Distance of point from lower end }\end{array}\right.\)
We can clearly see that elongation \(\propto\left(x^2\right)\)
So graph of \(\Delta x\) vs \(x\) should be a upward parabola.