Which series of the hydrogen spectrum lies in the visible region?

Hydrogen atoms are excited from the ground state to the principal quantum number $n = 5$. The number of spectral lines observed will be:

If the series limit frequency of the Lyman series is $v_L$,then the series limit frequency of the Pfund series is

Ratio of longest wavelengths corresponding to Lyman and Balmer series in hydrogen spectrum is :-

The first three spectral lines of the $H$-atom in the Balmer series are given as $\lambda_{1}, \lambda_{2}, \lambda_{3}$. Considering the Bohr atomic model,the wavelengths of the first and third spectral lines $\left(\frac{\lambda_{1}}{\lambda_{3}}\right)$ are related by a factor of approximately '$x$' $\times 10^{-1}$. The value of $x$,to the nearest integer,is:

The difference in the wavelength between the maximum and minimum of Balmer series [Use $R_{H} = 1 \times 10^7 \ m^{-1}$]. (in $Å$)