Which of the following is the radius of the first orbit of $He^{+}$ (in $pm$)?

The ratio of radii of the second orbit of a hydrogen atom to the fourth orbit of a $He^{+}$ ion is:

The frequency of the first line of the Paschen series in the spectrum of the $Be^{+3}$ ion is:

According to classical theory,the proposed circular path of an electron in Rutherford atomic model will be:

In a hydrogen atom,electrons are excited to the $5^{th}$ quantum level. How many different spectral lines may appear in the emission spectrum?

If change in energy $(\Delta E) = 3 \times 10^{-8} \ J$,$h = 6.64 \times 10^{-34} \ J \cdot s$ and $c = 3 \times 10^8 \ m/s$,then the wavelength of the light is: