energy level(2)

(a) 10.4 eV which is equal to 10.4 x 1.6x10^-19 J = 1.664 x 10^-18 J

(b) Energy released = (5.5 - 1.5) eV = 4 eV = 6.4 x 10^-19 J
frequency = 6.4x10^-19/6.63x10^-34 Hz = 9.65 x 10^14 Hz

(c) (i) electron transit from the -5.5 eV obit to the -1.5 eV orbit
(ii) electron is scattered with energy of 1eV
(iii) the atom is ionized.