Final answer:
The least effective reagent combination for generating sodium ethoxide, CH3CH2ONa, is Na2CO3 + CH3CH2Cl, as Na2CO3 is a weaker base and lacks the nucleophilicity to displace the chloride in an SN2 reaction.
Step-by-step explanation:
The question asks which combination of reagents is the least effective in generating sodium ethoxide, CH3CH2ONa. Among the given options, (d) Na2CO3 + CH3CH2Cl is the least effective method for producing sodium ethoxide. This is because sodium carbonate (Na2CO3) is a weak base and does not have the strong nucleophilic characteristics required to displace the chloride ion effectively in an SN2 reaction with an alkyl halide like ethyl chloride (CH3CH2Cl) to form sodium ethoxide. The other reagents (a) NaOH + CH3CH2Br, (b) Na + CH3CH2OH, and (c) NaH + CH3CH2I involve stronger nucleophiles or bases which are more capable of effectively generating sodium ethoxide.