In a hydrogen atom,if $9 \, eV$ of energy is supplied,how many spectral lines will be emitted?

Lifetimes of the molecules in the excited states are often measured by using pulsed radiation source of duration nearly in the nanosecond range. If the radiation source has the duration of $2 \, ns$ and the number of photons emitted during the pulse source is $2.5 \times 10^{15}$,calculate the energy of the source.

Which one of the following statements is not correct?

If the ionization potential of $Li^{2+}$ is $122.4 \ eV$,what is the $5^{th}$ ionization potential of carbon in $eV$?

$A$ $100 \ W$ bulb emits light of wavelength '$x$' $\mathring{A}$. What is the value of $x$, if the number of photons emitted is $2.0 \times 10^{20} \ s^{-1}$? $(h = 6.63 \times 10^{-34} \ J \cdot s, c = 3 \times 10^8 \ m \cdot s^{-1})$

Time taken for an electron to complete one revolution in the Bohr orbit of hydrogen atom is