Three photodiodes D1,D2 and D3 are made of semiconductors having band gaps of 2.5 eV, 2 eV and 3 eV respectively.  Which one will be able to detect of wavelength of 6000 Ao

For the incident radiation to be detected by the photodiode, energy of incident radiation should be greater than the band gap.Energy of photon = E=hceλ=6.6×10−34×3×1081.6×10−19×6×10−7=2.06 eVThis is true only for D2.