The Change in Energy of a One-Electron Atom or Ion $\Delta$

The change in energy of a one-electron atom or ion for an electronic transition from the initial energy level n_i to the final energy level n_f is given by $\Delta$ E = -(2.18 *10^-18 J) Z² Which of the following species will have the longest wavelength emission line for the transition between the n_i = 2 and n_f = 1 levels?

A) H
B) He⁺
C) Li²⁺
D) Be³⁺
E) B⁴⁺