Which of the following releases the smallest amount of energy upon gaining an electron?

$\ce{C}$, $\ce{Rb}$, $\ce{Ga}$, $\ce{Ge}$


I am confused in the sense that I don't know what it means by "released the smallest about of energy upon gaining?" would it be $\ce{Rb}$ because the shell is so big that when it loses an electron the overall energy doesn't really matter?




Alright, this is similar to a question that I have answered before but I will just give you the reasoning for this phenomenon. I will **not** give you the answer since this appears to be a homework question.


**Why an atom gains energy when you take off an electron?**
Well for this, think of the attractions between the nucleus and the electrons, so when you must ***strip*** away an electron from this stability, you must add energy to do so.


**Why an atom releases energy when you add an electron?**
This one might be a little hard to grasp, but at the end it is not too bad. Essentially the molecule is becoming more stable. It is getting near to having a full octet. (Ignoring noble gasses). In other words the kinetic energy added by gaining the electron is released when the atom is achieving a stable state. 


This is the general reasoning behind this, not too complicated, but I hope you will be able to understand it. Just, if you can't, remember the first one and think of the opposite for the second one. 




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Now, take a look at [this](https://chemistry.stackexchange.com/questions/30805/velocity-of-electrons-ejected-from-cl-atom/30813#30813) question, to help you with your question even more. You will then be able to deduce the correct answer.


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