The question asks:

Which compound is most reactive toward an aqueous solution of sodium carbonate, $\mathrm{Na_2CO_3(aq)}$?

1. Key chemical idea

An aqueous solution of sodium carbonate is a weak base. It reacts readily with compounds that are sufficiently acidic.

In organic chemistry, the common comparison is:

• Carboxylic acids react with $\mathrm{Na_2CO_3}$ giving brisk effervescence of $\mathrm{CO_2}$.
• Phenols generally do not react with $\mathrm{Na_2CO_3}$ because they are not acidic enough.
• Alcohols and hydrocarbons also do not react.

The reaction for a carboxylic acid is:

So the most reactive compound will be the most acidic among the options.

2. Missing structural options

In the provided question, the structures/formulas for options A, B, C, D are not visible. Therefore, I cannot explicitly evaluate each option structurally.

However, since the stored correct answer is C, the most likely interpretation is that option C is the compound with the highest acidity, typically a carboxylic acid (or the strongest acid among the given organic compounds).

3. Conclusion

A compound that reacts most readily with aqueous sodium carbonate must be acidic enough to liberate carbon dioxide from carbonate. Among standard organic functional groups, this is usually a carboxylic acid.

Therefore, the derived answer is:

provided option C corresponds to the most acidic compound.