Answer
(d) is correct.
Work Step by Step
The tension in the cord provides the centripetal force, so $$T=F_c=\frac{mv^2}{r}$$
$m$ and $v$ are the same for both stones, but $r_1=2r_2$. Therefore, $$\frac{T_1}{T_2}=\frac{\frac{mv^2}{r_1}}{\frac{mv^2}{r_2}}=\frac{r_2}{r_1}=\frac{1}{2}$$
(d) is correct.
