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

The circuit given represents which of the logic operations?

Identify the incorrect statement.

Three photodiodes $$D_1, D_2$$ and $$D_3$$ are made of semiconductors having band gaps of $$2.5 \mathrm{~eV}, 2 \mathrm{~eV}$$ and $$3 \mathrm{~eV}$$, respectively. Which one will be able to detect light of wavelength $$600 \mathrm{~nm}$$ ?