Answer: 5 → 2
Explanation: An electron when given enough energy will get excited to the higher states and when it returns to the ground state will emit energy in the from of light.
The most energetic energy level will be 5 → 2 because in this, energy level 2 is the ground state and energy level 5 is the excited state . Thus more energy will be needed by the electron to move towards the higher excited state.
The energy required by the 4 → 2 energy level will be of medium level and
3 → 2 will require the least energy.
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