Answer:
C. Copper
Explanation:
F = Force on string
[tex]L_0[/tex] = Intial length of string
A = Area of string
E = Young's modulus of material
Change in length is given by
[tex]\Delta L=\frac{FL_0}{AE}[/tex]
It can be seen that the change in length is inversely proportional to the Young's modulus of the material.
Here
[tex]E_a=0.7\times 10^{11}\ Pa[/tex]
[tex]E_b=0.91\times 10^{11}\ Pa[/tex]
[tex]E_c=1.1\times 10^{11}\ Pa[/tex]
[tex]\\\Rightarrow E_c>E_b>E_a[/tex]
So, copper will stretch the least.