Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

For example:

Answer: <most likely answer, as short as possible>.

Paragraph: 
When electrons are removed from an atom, that process requires energy to pull the electron away from the nucleus. Addition of an electron releases energy from the process.


Question: What is required when electrons are removed from an atom, and released from the process when an electron is added?
energy
Energy is required to remove electrons, released when electrons are added.