What is the angular momentum of an electron in the fourth orbit of a hydrogen atom?

$(i)$ The energy associated with the first orbit in the hydrogen atom is $-2.18 \times 10^{-18} \, J \, atom^{-1}$. What is the energy associated with the fifth orbit?
$(ii)$ Calculate the radius of Bohr's fifth orbit for the hydrogen atom.

In the Bohr series of lines of the hydrogen spectrum,the third line from the red end corresponds to which one of the following inter-orbit jumps of the electron for Bohr orbits in an atom of hydrogen?

The Bohr orbit radius for the hydrogen atom $(n = 1)$ is approximately $0.530 \ \mathring{A}$. The radius for the first excited state $(n = 2)$ orbit is ........... $\mathring{A}$

What is the number of photons of light with a wavelength of $4000 \ pm$ that provide $1 \ J$ of energy?

Assume that the radius of the first Bohr orbit of hydrogen atom is $0.6 \mathring{A}$. The radius of the third Bohr orbit of $He^{+}$ is $..................$ picometer. (Nearest Integer)