What is the packet of energy called?

Calculate the wavelength of the emitted radiation when an electron transitions from $n = 3$ to $n = 2$ in a hydrogen atom. To which region does this radiation belong?

In an electron transition from an infinite state to the ground state in an $H$ atom,find the emitted wavelength. (in $nm$)

Bohr’s atomic theory gave the idea of :

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 nuclear theory of the atom was put forward by: