$A$ photodiode is a device

Statement $-1$: $A$ photodiode operates in reverse bias.
Statement $-2$: The fractional change due to the photo-effects on the minority carrier dominated reverse bias current is more easily measurable than the fractional change in the forward bias current.

Which of the following statements is true about LEDs?

If a semiconductor photodiode can detect a photon with a maximum wavelength of $400\, nm$, then its band gap energy is (Given: Planck's constant $h = 6.63 \times 10^{-34}\, J \cdot s$, Speed of light $c = 3 \times 10^{8}\, m/s$) (in $ eV$)

Identify the devices which work on solar energy.
$(a)$ Photodiode
$(b)$ Photovoltaic cell
$(c)$ $LED$
$(d)$ Photo-thermal devices

The $I-V$ characteristics of an $LED$ are correctly shown by which graph?