Answer :
-- There are 80 protons in the nucleus of every atom of Mercury,
but only 8 of them in the nucleus of an atom of Oxygen.
-- Mercury must be warmer than 357°C in order to boil, but Oxygen
must only be warmer than -183°C.
-- Mercury must be colder than -39°C in order to freeze, but Oxygen
must be colder than -219°C.
-- Oxygen is required for human life. Mercury is a deadly poison.