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

For the wavelength of visible radiation of the hydrogen spectrum,Balmer gave an equation as $\lambda = \frac{(k m^2)}{(m^2 - 4)}$,where $m$ is an integer. The value of $k$ in terms of Rydberg's constant $R$ is

The electron in a hydrogen atom in a sample is in the $n^{th}$ excited state. The number of different spectral lines obtained in its emission spectrum will be:

If a hydrogen atom is excited from the ground state to another state with a principal quantum number $n = 4$,the number of spectral lines in the emission spectrum will be:

If $917 \mathring A$ is the lowest wavelength of the Lyman series,then the lowest wavelength of the Balmer series will be .......$\mathring A$.

In terms of Rydberg's constant $R,$ the wave number of the first Balmer line is