The radius of the first Bohr's orbit of the hydrogen atom is ............. $\mathring{A}$.

The energy of an electron in the first orbit of $He^{+}$ is $-871.6 \times 10^{-20} \ J$. What will be the energy of an electron in the first orbit of hydrogen?

If the wavelength of the first line in the Balmer series is $656 \ nm$,then the wavelength of its second line and limiting line respectively are

What is the ratio of the time period of revolution of an electron in the second orbit of a hydrogen atom to that in the third orbit of a $He^{+}$ ion?

What is the wave number of the lowest energy transition in the Balmer series?

If the radius of the second Bohr orbit of the $He^{+}$ ion is $105.8 \, pm$, what is the radius of the third Bohr orbit of the $Li^{2+}$ ion?