In 1953, S.L. Miller created electric discharge in a closed flask to…

The correct answer is Option (1) → CH₄, H₂, NH₃ and water vapour

Oparin and Haldane proposed that the first life came from non-living organic molecules, formed earlier from simple inorganic substances (chemical evolution). The early earth had high temperature, volcanic storms and a reducing atmosphere containing methane and ammonia. In 1953, S.L. Miller recreated these conditions: he passed electric discharge through a closed flask of methane, hydrogen, ammonia and water vapour and obtained amino acids.

Option (1) CH₄, H₂, NH₃ and water vapour — Correct. These four are the gases of Miller’s flask. Methane (CH₄), hydrogen (H₂), ammonia (NH₃) and water vapour together give a reducing mixture, like the early earth’s atmosphere.

Option (2) CH₄, O₂, NH₃ and water vapour — Incorrect. Oxygen (O₂) was not in the flask; hydrogen was. Free oxygen would make the mixture oxidising, unlike the reducing atmosphere the experiment set out to copy.

Option (3) CO₂, H₂, N₂ and water vapour — Incorrect. Carbon dioxide (CO₂) and nitrogen (N₂) were not used. This mixture also lacks methane and ammonia, the two gases the book names for the early atmosphere.

Option (4) CH₄, H₂, O₂ and CO₂ — Incorrect. This mixture has oxygen and carbon dioxide and no ammonia. Without ammonia there would be no nitrogen source for forming amino acids.

Figure 6.1 Diagrammatic representation of Miller’s experiment

NCERT Extract:
Origin of Life – “… The conditions on earth were – high temperature, volcanic storms, reducing atmosphere containing CH₄, NH₃, etc. In 1953, S.L. Miller, an American scientist created similar conditions in a laboratory scale (Figure 6.1). He created electric discharge in a closed flask containing CH₄, H₂, NH₃ and water vapour at 800^oC. He observed formation of amino acids.”