Combination of NAND gates is shown in the figure. It is equivalent to

In an ideal junction diode, the current flowing through PQ is

LED is manufactured using zinc selenide then it emits.

In a pure silicon, number of electrons and holes per unit volume are $$1.6 \times 10^{16} \mathrm{~m}^{-3}$$. If silicon is doped with Boron in a way that on doping hole density increases to $$4 \times 10^{22} \mathrm{~m}^{-3}$$. Then electron density in doped semiconductor will be