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

In a hydrogen atom,the energy difference between the states $n = 2$ and $n = 3$ is $E \ eV$. The ionization energy of the $H$-atom is: (in $E$)

The energy of an electron in an excited hydrogen atom is $-3.4 \, eV$. According to Bohr's theory,the angular momentum of this electron in $J \cdot s$ is:

When a metal surface is irradiated with light of frequency $x \ Hz$,the kinetic energy of emitted photoelectrons is $z \ J$. When the same metal is irradiated with light of frequency $y \ Hz$,the kinetic energy of emitted electrons is $\frac{z}{3} \ J$. What is the threshold frequency (in $Hz$) of the metal?

The postulate of Bohr theory that electrons jump from one orbit to the other,rather than flow,is according to:

Find the energy of each of the photons which:
$(i)$ correspond to light of frequency $3 \times 10^{15} \, Hz$
$(ii)$ have a wavelength of $0.50 \, \mathring{A}$