Concept:Free radical halogenation of alkanes can produce a mixture of substituted products, but the ratio of reactants controls which product dominates.
Explanation:When methane reacts with chlorine gas in the presence of UV light, chlorine radicals replace hydrogen atoms one by one.
The possible products are chloromethane (
CH3​Cl), dichloromethane (
CH2​Cl2​), trichloromethane (
CHCl3​), and tetrachloromethane (
CCl4​).
Because methane is taken in excess, the concentration of methane is very high compared to chlorine.
The chloromethyl radical formed first quickly collides with a methane molecule to form chloromethane, so further chlorination is suppressed.
Additionally, chlorine is limited, which means insufficient chlorine is available for the later substitution steps.
As a result, monochlorination is favoured, and chloromethane is obtained as the major product.
On the other hand, if excess chlorine were used, tetrachloromethane would be the major product.
Answer:Option A. Chloromethane