$750$ waves of an electromagnetic radiation pass a point in one minute. What is the wavelength of the radiation?

The energy of an electromagnetic radiation is $19.875 \times 10^{-13} \ erg$. What is its wave number in $cm^{-1}$? $(h = 6.625 \times 10^{-27} \ erg \ sec, c = 3 \times 10^{10} \ cm \ sec^{-1})$

Consider a helium $(He)$ atom that absorbs a photon of wavelength $330 \ nm$. The change in the velocity (in $cm \ s^{-1}$) of the $He$ atom after the photon absorption is . . . . . .
(Assume: Momentum is conserved when the photon is absorbed. Use: Planck constant $= 6.6 \times 10^{-34} \ J \ s$,Avogadro number $= 6 \times 10^{23} \ mol^{-1}$,Molar mass of $He = 4 \ g \ mol^{-1}$)

Consider two radiations of wavelengths $1. \lambda_1 = 2000 \mathring{A}$ and $2. \lambda_2 = 6000 \mathring{A}$. The ratio of the energies of these two radiations $\left(\frac{E_1}{E_2}\right)$ is . . . . . . (Nearest integer).

$A$ hypothetical electromagnetic wave is shown below. The frequency of the wave is $x \times 10^{19} \ Hz$. $x =$ . . . . (nearest integer)

Nitrogen laser produces a radiation at a wavelength of $337.1 \ nm$. If the number of photons emitted is $5.6 \times 10^{24}$,calculate the power of this laser.