In a hydrogen atom,electrons are excited to the $5^{th}$ quantum level. How many different spectral lines may appear in the emission spectrum?

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 maximum energy is present in any electron at

The radius of the first orbit of $Li^{2+}$ is $X \mathring{A}$. The radius of the third orbit of $He^{+}$ (in $\mathring{A}$) is (in $X$)

The ionisation potential of a hydrogen atom is $-13.6 \ eV$. What will be the energy of the atom corresponding to $n = 2$?

Write down the observations and conclusions of the $\alpha$-particle scattering experiment.