Explanation

(d)
We know that $E_{n} \propto \left\lbrack - \frac{1}{n^{2}} \right\rbrack,$ where $n$ is the number of orbit.
Hence, as the value of $n$ increases, energy of the electron also increases. Hence, when $n$ becomes infinite, energy also becomes infinite. Hence, due to this reason maximum energy is possessed by an electron, when it is present at infinite distance from the nucleus.