Hydrogen Atom Questions

The ground state energy of hydrogen atom is $-13.6\text{eV}$. What is the potential energy of the electron in this state?

The ground state energy of hydrogen atom is $-13.6\text{eV}$. When its electron is in the first excited state, its excitation energy is:

Hydrogen atom in ground state is excited by a monochromatic radiation of $\lambda =975\text{A˚}$. Number of spectral lines in the resulting spectrum emitted will be: