Number of waves formed by a Bohr electron in one complete revolution in its third orbit is

What should be the momentum (in $g \ cm / s$) of a particle if its de Broglie wavelength is $1 \ \mathring{A}$ and the value of $h$ is $6.6252 \times 10^{-27} \ erg \ s$?

The wavelength of the electron in the ground state of a hydrogen atom is $y \ \mathring{A}$. What is the wavelength of the electron in the fourth orbit of $He^{+}$ ion (in $\mathring{A}$)?

The mass of an electron is $9.1 \times 10^{-31} \ kg$. If its $K.E.$ is $3.0 \times 10^{-25} \ J$,calculate its wavelength.

The wavelength of the electron emitted by a metal sheet of work function $4 \ eV$ when photons from $EMR$ of wavelength $124 \ nm$ strike the metal plate is ........... $nm$.

Which one of the following explains light both as a stream of particles and as wave motion?