Step 1: Understanding the relationship between wave velocity and stress.
The wave velocity \( V \) on a stretched string is given by:
\[
V = \sqrt{\frac{T}{\rho}}
\]
Where:
- \( T \) is the tensile stress,
- \( \rho \) is the density.
Rearranging the equation for stress \( T \), we get:
\[
T = \rho V^2
\]
Thus, the correct answer is (D) \( V^2 \rho \).