Which energy level of the singly ionized carbon atom has the same energy as the ground state energy of the hydrogen atom?

The energy of an electron in the fourth excited state of the hydrogen atom is

An electron makes a transition from an excited state to the ground state of a hydrogen-like atom. Out of the following statements,which one is correct?

Energy of $H$-atom in the ground state is $-13.6 \; eV$. The energy needed to ionize a hydrogen atom which is in its second excited state is ....... $eV$.

In a hydrogen-like atom,an electron makes a transition from an energy level with principal quantum number $n$ to another with principal quantum number $(n - 1)$. If $n >> 1$,the frequency of the emitted radiation is proportional to:

Energy of a stationary electron in the hydrogen atom is $E = -\frac{13.6}{n^2} \text{ eV}$. Calculate the energies required to excite the electron in a hydrogen atom to $(a)$ its second excited state and $(b)$ its ionized state,respectively.