Correct Answer - B
Consider a ase of an n type semi-conductor te majority carries density (n) is considerably larger than the minority hole density `rho` (i.e., n gt gt p). On illumination `n_(f)=n+Deltan` & `p_(f)=p+Deltap`
since `Deltan=Deltap` {equal hole electron pair generation in bond breaking]
`(Deltan)/(n)lt lt (Deltap)/(p)`
`therefore` it is difficult to measure small `(Deltan)/(n)`
Compared to `Deltap//p`
`therefore` Photodiode is used in Reverse bios mode since it is easier to measure the higher fractional change of minority carriers.