The gas that makes up about 12 percent of the earths atmosphere is ?

You may be referring to the gas that makes up 21% of the earth's atmosphere, which is oxygen.

Explanation:

According to NASA, the gases in Earth's atmosphere include:

Nitrogen — 78 percent

Oxygen — 21 percent

Argon — 0.93 percent

Carbon dioxide — 0.04 percent

(Trace amounts of neon, helium, methane, krypton and hydrogen, as well as water vapor)

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.

i believe the answer is 5,000