The correct option is C 2 : 1 : 2
Stanley miller and Harold urey conducted an experiment in which they recreated the primitive earth like atmosphere to explain how chemical evolution was a precursor for biological evolution. In this experiment,high electric voltage was applied on mixture of CH3,NH3,H2 and water vapour by which they were able to synthesize amino acids. The ratio of methane, ammonia and hydrogen was 2:1:2. So, the correct answer is '2:1:2'.