Final answer:
In electron transitions, absorption of energy leads to higher energy states, while release of energy leads to lower energy states.
Step-by-step explanation:
In electron transitions, the absorption or emission of radiation involves a change in energy levels. When an electron transitions from a lower energy level to a higher energy level, it absorbs energy and is said to be in an excited state (e.g., A absorbs energy and goes to a higher energy state, N=1 to N=5). On the other hand, when an electron transitions from a higher energy level to a lower energy level, it releases energy and returns to a lower energy state (e.g., B releases energy and goes to a lower energy state, N=5 to N=3).
The same concept applies to C and D. In C, the transition from N=3 to N=5 involves the absorption of energy, taking the electron to a higher energy state. In D, the transition from N=5 to N=1 involves the release of energy, bringing the electron to a lower energy state.