Which of the following relations is correct for a photon?

If $E$ and $P$ are the energy and the momentum of a photon respectively,then on reducing the wavelength of the photon:

The energy of a photon of wavelength $\lambda$ is given by

The frequency of a photon having energy $100 \ eV$ is $(h = 6.6 \times 10^{-34} \ J \cdot s)$.

Two sources of light emit with a power of $200 \ W$. The ratio of the number of photons of visible light emitted per second by each source having wavelengths $300 \ nm$ and $500 \ nm$ respectively,will be:

The principle of $LASER$ action involves: