All the energy levels in a simple model of an atom are shown.

The atom is excited so that an electron is promoted to the \( - {\text{0.50 eV}}\) energy level. How many different frequencies will be observed in the emission spectrum?

A.     3

B.     4

C.     5

D.     6

B

More than half of the candidates chose A, suggesting that they did not understand that the emission spectrum contained evidence of all possible electron transitions. Normally with four energy levels this would involve 6 transitions, but in this case some of the transitions were identical – a fact that escaped most candidates even the most able.