When an excited electron in an atom moves to the ground state, the electron
(1) absorbs energy as it moves to a higher energy state
(2) absorbs energy as it moves to a lower energy state
(3) emits energy as it moves to a higher energy : state
(4) emits energy as it moves to a lower energy state

Answer is: (4) emits energy as it moves to a lower energy state.

Atom emits a characteristic set of discrete wavelengths, according to its electronic energy levels.

Emission spectrum of a chemical element is the spectrum of frequencies emitted due to an atom making a transition from a high energy state to a lower energy state.  

Each transition has a specific energy difference.  

Each element's emission spectrum is unique.

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water pollution kills aquatic life. aquatic life includes algae and other plant life that use photosynthesis. photosynthesis takes   c02 out of the air.  

c02is a greenhouse gas.

answer; natural resources;