The ratio of the time period of an electron in the first and third orbit of an $H$-atom would be:

If the shortest wavelength of the $He^{+}$ ion in the Balmer series is $X \ m$,then the longest wavelength in the Paschen series of the $Li^{2+}$ ion is:

Match List-$I$ with List-$II$.

List-$I$ (Spectral Series for Hydrogen)	List-$II$ (Spectral Region)
$A$. Lyman	$I$. Infrared region
$B$. Balmer	$II$. $UV$ region
$C$. Paschen	$III$. Infrared region
$D$. Pfund	$IV$. Visible region

Choose the correct answer from the options given below:

The frequency of radiation emitted when the electron falls from $n = 4$ to $n = 1$ in a hydrogen atom will be (Given ionization energy of $H = 2.18 \times 10^{-18} \ J \ atom^{-1}$ and $h = 6.625 \times 10^{-34} \ Js$)

When an electron jumps from $n = 5$ to $n = 2$ with all possible transitions,which of the following statements is correct?

What is the ratio of the radii of the second orbit for $H$,$He^{+}$,and $Li^{2+}$?