The velocity of an electron in the first Bohr orbit of $He^+$ ion is .......

In Bohr's model of hydrogen-like species,which of the following is true?

The ratio of the velocity of the electron in the first Bohr orbit to that in the second Bohr orbit of a hydrogen atom is

An electron rotates in a circle around a nucleus having positive charge $Ze$. The correct relation between the total energy $(E)$ of the electron and its potential energy $(U)$ is:

Find the radius of $Be^{3+}$ ions in its ground state assuming Bohr's model to be valid $(a_0 = 53 \ pm)$. (in $pm$)

$A$ hydrogen atom is in the ground state. In order to get six lines in its emission spectrum,the wavelength of the incident radiation should be .......... $\mathring A$.