When using NaHCO3 for extraction, which species will be found in the aqueous layer?

When using NaHCO₃ (sodium bicarbonate) for extraction, the aqueous layer will contain the ionic form of X. This is due to the nature of NaHCO₃ being a weak base that can deprotonate certain acidic compounds, converting them from their neutral form to their ionic form.

During the extraction process, if Mixture X contains an acidic component, it can react with NaHCO₃. The weak base will facilitate the deprotonation of any acidic moieties in Mixture X, resulting in the formation of carboxylate ions or other ionic species. These ionic forms are more soluble in the aqueous layer compared to their neutral forms, which tend to prefer the organic layer during extraction.

In contrast, 4-bromophenol, being a relatively weak acid, would also be converted to its ionic form in the presence of NaHCO₃. However, if the question specifically refers to Mixture X and its ionic form, this indicates that Mixture X contains an acidic component that is effectively affected by the presence of NaHCO₃, leading to the correct answer being the ionic form of X found in the aqueous layer.