What kind of $p-n$ junction diode does not require any kind of bias?

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

Identify the mismatch out of the following.

$A$ photodetector is fabricated from a semiconductor with a band gap $E_g = 0.73 \, eV$. What is the maximum wavelength (in $nm$) it can detect?

The $I-V$ characteristics for a junction diode are shown. The device is

The maximum rated power of the $LED$ is $2 \text{ mW}$ and it is used in the circuit with an input voltage of $5 \text{ V}$ as shown in the figure. The Zener diode has a breakdown voltage of $1 \text{ V}$. The current through the resistance $R = 1 \text{ k}\Omega$ is $0.5 \text{ mA}$. The minimum value of the resistance $R_S$ to ensure that the $LED$ is not damaged is . . . . . . $\text{k}\Omega$.