Correct Answer - d
Charge responsible for producing flux in the shell `=q//3`. In this case, angle formed by the shell at centre of ring `(q)/(3 epsilon_(0))`
So, charge to contribute flux in the shell
`=(2pi)/(3)(q)/(2pi)= (q)/(3)`
It is possible only if radii of ring and shell are equal and circumference of each passes through the centre of the other.
So, radius of ring `R`