Oil floats on the surface of water but mercury sinks. why?

Because if the object weighs more than the volume when it is placed in the water it will sink. If this object weighs less than the volume of water, it will float. This depends mostly on the type of item.

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