Answer:
The radius is

Step-by-step explanation:
From the question we are told that
The distance beneath the liquid is

The refractive index of the liquid is

Now the critical value is mathematically represented as
![\theta = sin ^(-1) [(1)/(n_i) ]](https://img.qammunity.org/2021/formulas/physics/college/eajws0sx8gs71pykg5anv076n83pycsabh.png)
substituting values
![\theta = sin ^(-1) [(1)/(131) ]](https://img.qammunity.org/2021/formulas/physics/college/kbjl9mkc070begdg5hp2dxtmu7j48yym6q.png)

Using SOHCAHTOA rule we have that

=>

substituting values

