Explanation

(b)
$C_{2}H_{5}O^{-}$ will attract the proton from phenol converting the later into phenoxide ion. This would then make nucleophilic attack on the methylene carbon of alkyl iodide, but $C_{2}H_{5}O^{-}$ is in excess $C_{2}H_{5}O^{-}$ is better nucleophile than $C_{6}H_{5}O^{-}$(phenoxide) ion since while in the former the negative charge is localised over oxygen and in the later it is delocalised over the whole molecular frame work. So, it is $C_{2}H_{5}O^{-}$ ion that would make nucleophilic attack at ethyl iodide to give diethyl ether (Williamson’s synthesis).
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