In the figure, which of the diode is in reverse bias

Which of the following is in reverse bias:

The current in the forward bias is unknown to be more (~mA) than the current in the reverse bias ( ~muA ). What is the reason then to operate the photo diodes in reverse bias ?

In the figure the emitter forward bias or reverse bias?

If a p-n junction diode is in reversed bias

The current in the forward bias is known to be more (mA) than the current in the reverse bias ( ~ mu A). What is the reason, then why photo diodes is to operate in reverse bias.

The V-I characteristic of a diode is shown in the figure. The ratio of forward to reverse bias resistance is

The V-I characteristic of a diode is shown in the figure. The ratio of forward to reverse bias resistance is

The V-I characteristic of a diode is shown in the figure. The ratio of forward to reverse bias resistance is