Complementary angles supplementary angles right angles vertical angles

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

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