Correct Answer - `sqrt(2)`
As `PQ` is normal to `AB`,
`:. i_(1) = 0, r_(1) = 0`
The ray goes straight along `PQR`. At `R, sqrt(i) = 45^(@)` which is critical angle of material of the prism.
Therefore, `QR` suffers total internal reflection at `R` and goes along `RS`
`mu = (1)/(sin C) = (1)/(sin 45^(@)) = (1)/(1//sqrt(2)) = sqrt(2)`