Which sentence describes all atoms of one element? 1.) they have the same number of isotopes?
2.) they have the same number of neutrons?
3.) they have the same number of electrons?
4.) they have the same number of protons?

4. they have the same number of protons

Explanation:

while all the other particles and attributes can be changed, protons cannot.

answer:

the answer is 6 valence electrons.

explanation:

valence is the # of electrons on the outer most shell of an atom.

oxygen has 6.

although, the valency of oxygen is 2, because it only needs to make 2 covalent bonds, or gain 2 electrons, to achieve the stable octet configuration of a noble gas.

that's it!

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~ trueboss72