What is the ratio of the radii of the second orbit for $H$,$He^{+}$,and $Li^{2+}$?

Supposing the energy (in arbitrary units) of the energy levels in the hydrogen atom is given as under:

Energy level	$K$ $(n=1)$	$L$ $(n=2)$	$M$ $(n=3)$	$N$ $(n=4...n=\infty)$
Energy	$-864 \ a.u.$	$-216 \ a.u.$	$-96 \ a.u.$	$0 \ a.u.$

The excitation energy needed to raise the electron from $M$ level to $n = \infty$ would be:

If the speed of an electron in the Bohr's first orbit of a hydrogen atom is $x$,the speed of the electron in the third Bohr's orbit is:

Following results are observed when sodium metal is irradiated with different wavelengths. Calculate $(a)$ threshold wavelength and $(b)$ Planck's constant.

$\lambda \ (nm)$	$500, 450, 400$
$v \times 10^{-5} \ (cm \ s^{-1})$	$2.55, 4.35, 5.35$

For the hydrogen emission spectrum,the energy change $E$ (in Joules) is given by $\Delta E = 2.18 \times 10^{-18} \left( \frac{1}{n_1^2} - \frac{1}{n_2^2} \right) \ J$,where $n_1 = 1, 2, 3, \dots$ and $n_2 = 2, 3, 4, \dots$. Which of the following corresponds to the Paschen series?

Observe the following statements:
Statement-$I$: Rutherford model of an atom cannot explain the stability of an atom.
Statement-$II$: The wavelength of $X$-rays is higher than the wavelength of microwaves.
The correct answer is: