Question

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

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

Answer 1

The correct option is D $O_2$

Conditions on primitive earth

• Primitive Earth had large number of atoms like hydrogen, carbon, oxygen, nitrogen, phosphorus etc
• These atoms combined to form simple molecules.
• Hydrogen atoms were most abundant and it combined with oxygen and nitrogen forming water and ammonia respectively.
• The atmosphere was reducing in nature. Hence oxygen was absent at the time of origin of life.

Final answer
(c) $O_2$