Which of the following could
be comprised of one atom?
a. carbon
b. salt
c. air

Carbon is Carbon so it's just one atom.

Air is mostly O2, N2, H2O and

Salt is NaCl and not one atom ;)

format change of dna.  

it would affect precipitation by causing flooding in some areas of the world due to climate increasing, causing the glaciers in the northern and southern pole of our planet to melt.

i wish you would have provided choices to simplify it and allow me to give an exact answer.