The eyes of certain reptiles pass a single visual signal to the brain, where the visual receptors are struck by photons with a wavelength of 850 nm. if a total energy of 3.15 x 10⁻¹⁴ j is required to trip the signal, what is the minimum number of photons that must strike the receptor?

135000photons

Explanation:

The total energy of all the photons was given in the question. Since the wavelength was given, we can use it to find the individual energy of each photon. Then having found the energy of one photon we can now relate it to the total energy photons striking the receptors and hence find the number of photons having that total energy. This is the total number of photons striking the receptors.

it's all four options.