The visible range of the hydrogen spectrum contains which of the following series?

The difference between the radii of $3^{rd}$ and $2^{nd}$ orbit of $H$ atom is $x \text{ pm}$. The difference between the radii of $4^{th}$ and $3^{rd}$ orbit of $Li^{2+}$ ion is $y \text{ pm}$. The ratio $y:x$ is equal to:

The energy of an electron in the $n^{th}$ orbit of a hydrogen atom is given by:

The energy associated with the first orbit of $He^{+}$ is

The spectrum of $Li^{2+}$ is similar to that of:

Which transition in the hydrogen spectrum would have the same wavelength as the Balmer type transition from $n = 4$ to $n = 2$ of $He^+$ spectrum?