Of those listed which gas is the least abundant in earths atmospherea- oxygen  b- nitrogen  c- ozoned - argon 

Option C = Ozone

Explanation:

The Percentage of given gases in atmosphere:

Oxygen = O₂ = 20.95 %

Nitrogen = N₂ = 78.08%

Argon = Ar = 0.93%

Ozone = O₃ = 0.000004%

Nitrogen is most abundant gas in atmosphere while oxygen is second most abundant gas. The nitrogen and oxygen are present in diatomic form such as O₂ and N₂.

Water vapors are also present but the percentage vary according to location. In hot humid areas the percentage of water is 0- 4% and it is third abundant gas.

The percentage of other gases in atmosphere are given below:

CO₂ = 0.0360%

Ne = 0.0018%

He = 0.0005%

CH₄ = 0.00017 %

N₂O = 0.0003%

H₂ = 0.00005%

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands