The primitive reducing atmosphere of earth was rich in water vapour, carbon monoxide, carbon dioxide and hydrogen. Absorption of infrared radiation by green house gases (CO2 and CH4) imparted high temperature to primitive earth. The high temperature, UV light and lightening facilitated reaction between above mentioned gases. Oxygen did not occur in the free state as the prevailing reduced substances immediately combined with it to form oxides (iron oxides, silicon oxides). Abundant hydrogen combined with free oxygen, nitrogen and carbon to form water, ammonia, methane and cyanides. Thus, the correct answer is option D.