Which logic gate is represented by the following combination logic gates?

An LED is constructed from a $$p$$-$$n$$ junction diode using GaAsP. The energy gap is $$1.9 \mathrm{~eV}$$. The wavelength of the light emitted will be equal to

The energy gap between valance band and the conduction band for a given material is $$6 \mathrm{~eV}$$, then the material is :

In the given circuit the diode $$D_1$$ and $$D_2$$ have the forward resistance $$25 \Omega$$ and infinite backward resistance. When they are connected to the source as shown, the current passing through the $$175 \Omega$$ resistor is: