If the velocity of an electron in the $n^{th}$ orbit of a Bohr atom is $v$,what is the value of $n$?

Write down the limitations of Bohr's model.

Based on equation $E = - 2.178 \times 10^{-18} \ J \left( \frac{Z^2}{n^2} \right)$,certain conclusions are written. Which of them is not correct?

The ionization energy of a hydrogen atom is $13.6 \, eV$. What is the energy required (in $eV$) to excite the electron from the ground state to the first excited state?

The energy of an electron in the excited hydrogen atom is $-3.4 \ eV$. Then according to Bohr's theory,the angular momentum of the electron in that excited state is ($h=$ Planck's constant).

The difference between the radii of $3^{rd}$ and $4^{th}$ orbits of $Li^{2+}$ is $\Delta R_{1}$. The difference between the radii of $3^{rd}$ and $4^{th}$ orbits of $He^{+}$ is $\Delta R_{2}$. Ratio $\Delta R_{1} : \Delta R_{2}$ is :