If the potential energy of the electron is $-10 \ eV$,what is the total energy in $eV$?

The radius of the first excited state of a Helium ion $(He^+)$ is given by (where $a_0$ is the radius of the first stationary state of the hydrogen atom):

Which of the following results is not true about the photoelectric effect?

In Rutherford's experiment,generally the thin foil of heavy atoms,like gold,platinum etc. have been used to be bombarded by the $\alpha$-particles. If the thin foil of light atoms like Aluminium etc. is used,what difference would be observed from the above results?

Which of the following represents the velocity of an electron in a hydrogen-like atom?

Which of the following transitions has the minimum wavelength?