(d) Fundamental frequency,
$v = \frac{1}{2l}\sqrt{\frac{T}{m}} = \frac{1}{2l}\sqrt{\frac{T}{\pi r^{2}\rho}}\ $
$or\ \ \ \ v \propto \frac{1}{lr}$
$\therefore\ \frac{v_{1}}{v_{2}} = \frac{l_{2}r_{2}}{l_{1}r_{1}} = \frac{2L \times r}{L \times 2r} = 1$