Question

Which was absent in the atmosphere at the time of origin of life?

• A.
  $N{H}_3$
• B.
  $H_2$
• C.
  $O_2$
• D.
  $C{H}_4$

Answer 1

The correct option is C

$O_2$
Gases that were present at the time of origin of life are ammonia, hydrogen, nitrogen, carbon dioxide, methane, and water vapour. Oxygen was formed at a very later stage.
Therefore, the gas which was absent at the time of origin of the earth is oxygen.