The ratio of the radius of the first Bohr orbit to that of the second Bohr orbit of the orbital electron is

The ratio of centripetal acceleration for an electron revolving in the $3^{\text{rd}}$ orbit to the $5^{\text{th}}$ Bohr orbit of a hydrogen atom is:

The radius of the first orbit of hydrogen is $r_{H}$,and the energy in the ground state is $-13.6 \text{ eV}$. Considering a $\mu^{-}$-particle with a mass $207 m_e$ revolving around a proton as in a hydrogen atom,the energy and radius of the proton and $\mu^{-}$-combination respectively in the first orbit are (assume the nucleus to be stationary):

If the radius of a hydrogen atom in its first orbit is $a_{0}$,then its radius in the third excited state is . . . . . . . (in $a_{0}$)

According to Bohr's model, the radius of the second orbit of a helium ion $(He^+)$ is ........ $\mathring{A}$.

In the Bohr model of the hydrogen atom, the electron is pictured to rotate in a circular orbit of radius $5 \times 10^{-11} \, m$, at a speed of $2.2 \times 10^{6} \, m/s$. What is the current associated with the electron's motion (in $ \, mA$)?