What is a photon?

The minimum intensity of light that can be perceived by the human eye is $10^{-10} \ W/m^2$. If the area of the pupil is $10^{-6} \ m^2$ and the wavelength of light is $560 \ nm$,approximately how many photons per second enter the eye? (Use $h = 6.6 \times 10^{-34} \ J \cdot s$ and $c = 3 \times 10^8 \ m/s$).

Write the characteristics of a photon or how can a photon of electromagnetic radiation be represented?

Which one of these is non-divisible?

If the energy of a photon corresponding to a wavelength of $6000 \mathring{A}$ is $3.2 \times 10^{-19} \ J$,the photon energy for a wavelength of $4000 \mathring{A}$ will be . . . . . . .

If the energy of a photon is $E$ and its momentum is $p$,given by the relations $E = h\nu$ and $p = h/\lambda$,what is the velocity of the photon?