Nature of Electromagnetic Radiation

In a sample of $\mathrm{H}-$atom, electrons make transition from $5^{\text{th }}$ excited state to ground state, producing all possible types of photons, then number of lines in infrared region are:

A bulb of $40 \mathrm{W}$ is producing a light of wavelength $620 \mathrm{nm}$ with $80 \%$ of efficiency, then the number of photons emitted by the bulb in $20$ seconds are: $\left(1 \mathrm{eV}=1.6\times {10}^{-19} \mathrm{J}, \mathrm{hc}=12400 \mathrm{eV} \mathrm{\AA })\right.$

Electromagnetic radiations of wavelength $242 \mathrm{nm}$ is just sufficient to ionise sodium atom. Then, the ionisation energy of Sodium in $\mathrm{kJ}$ ${\mathrm{mole}}^{-1}$ is:

Photon of which light has maximum energy?

The MRI (magnetic resonance imaging) body scanners used in hospitals operate with $400 \mathrm{MHz}$ radio frequency energy. The wavelength corresponding to this radio frequency is:

The ratio of energy of a photon of wavelength $2000\stackrel{°}{\mathrm{A}}$ to that of one with wavelength $4000\stackrel{°}{\mathrm{A} }$is____.

The value of Planck's constant is $6.3\times {10}^{-34} \mathrm{Js}$. The velocity of light is $3\times {10}^8 \mathrm{m} {\sec }^{-1}$. Which value is closest to the wavelength of a quantum of light with frequency of $8\times {10}^{15} {\sec }^{-1}$?

A gas absorbs a photon of $355 \mathrm{nm}$ and emits at two wavelengths. If one of the emissions is at $680 \mathrm{nm}$, the other is at :