What combines to form compounds? a.) molecules b.) atoms of element c.) minerals d.) valences

Hello! Glad to help.

From what I have learned in my ICP class, molecules combine together to form componds.  A compound is any molecule that is made up of two or more different elemental atoms.

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the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.