Joining together two COMPLETE phrases.
When joining together two sentences with a conjunction, you would use a comma.
It wouldn't be used to describe a list or show that someone is stuttering.
I hope this helps!
~cupcake
Answer:
Selenium atoms have 34 electrons and the shell structure is 2.8. 18.6. The ground state electron configuration of ground state gaseous neutral selenium is [Ar].
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