In the atomic spectrum of hydrogen,the series of lines observed in the visible region is:

In a hydrogen atom,the energy of an $e^-$ in an orbital is given by $E = \frac{-constant}{n^2} \ (kJ \ mol^{-1})$. Which of the following properties is constant according to the given equation?

The energy of a photon is $3 \times 10^{-12} \ erg$. What is its wavelength in $nm$? $(h = 6.62 \times 10^{-27} \ erg \cdot s; \ c = 3 \times 10^{10} \ cm/s)$

Write down the observations and conclusions of the $\alpha$-particle scattering experiment.

An excited hydrogen atom emits light in the ultraviolet region at a frequency of $2.47 \times 10^{15} \ Hz$. Calculate the energy of a single photon. (Given: $h = 6.63 \times 10^{-34} \ J \cdot s$)

The radii of the first Bohr orbit of $H$ $(r_{H})$,$He^{+}$ $(r_{He^{+}})$ and $Li^{2+}$ $(r_{Li^{2+}})$ are in the order