The electron in the hydrogen atom undergoes a transition from higher orbitals to an orbital of radius $211.6 \text{ pm}$. This transition is associated with:

The visible range of the hydrogen spectrum contains which of the following series?

What is the maximum number of different spectral lines obtained when a sample of a large number of $H$-atoms in the $5^{th}$ excited state makes transitions to the ground state,given that no lines are emitted in the Balmer series?

The work function of a metal is $4.2 \, eV$. If radiation of $2000 \, \mathring{A}$ falls on the metal,then the kinetic energy of the fastest photoelectron is:

$A$ certain metal has a work function of $\Phi = 2 \ eV$. It is irradiated first with $1 \ W$ of $400 \ nm$ light and later with $1 \ W$ of $800 \ nm$ light. Among the following,the correct statement is
[Given: Planck constant $(h) = 6.626 \times 10^{-34} \ J \ s$;
Speed of light $(c) = 3 \times 10^8 \ m \ s^{-1}$ ]

What is the ratio of the radius of the second Bohr orbit to the first Bohr orbit of the $H$ atom?