Question

how much energy is needed to completely remove an electron from n=4?

Answer 1

Energy required is
\[E_\infty -E_4\]

\[E_ \infty=0\]
\[E_4=13.6/4^2\]

therefore E= Do the calculation.

Answer 2

\[E_n=13.6/n^2\]

Answer 3

@talita did you understand this.

Answer 4

@praxer

That only works for hydrogen :P

Answer 5

^^ This is much important.
It would depend on the electron config of the atom.