Answer:
In its stable molecular form, oxygen exists as two atoms and is written O2. to distinguish it from an atom of oxygen O, or ozone, a molecule of three oxygen atoms, O3. Even though each of these is all oxygen, combining atoms of the same element may give very different properties to the molecule.
Explanation:
D, or the 4th one. It combines the sentences effectively, without overusing words.
Answer:c
Explanation:a visible sign left behind after something no longer exists
