Which of the following would be the most difficult to compress?
a)oxygen
b)water
c)brick
d)salt water

Brick

Explanation:

The brick is already the most dense.

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.