In acyl compounds ( i.e. acyl chloride, acid anhydride, ester and amide ) $$RCO-$$  group is same, thus reactivity depends upon the nature of group $$Z$$ \[\left( i.e.\,\,C{{l}^{-}},RCO{{O}^{-}},R'{{O}^{-}},NH_{2}^{-},etc. \right)\]
If group $$Z$$ is a weak base, then it is a strong leaving agent and its reactivity towards nucleophilic substitution is high.
The order of basic nature of $$Z$$ groups is
$$C{l^ - } < RCO{O^ - } < R'{O^ - } > NH_2^ - $$
Thus, order of reactivity is
$$\mathop {RCOCl}\limits_{{\text{Acyl chloride}}} > \mathop {{{\left( {RCO} \right)}_2}O}\limits_{{\text{Acid anhydride}}} > \mathop {RCOOR'}\limits_{{\text{Ester}}} > \mathop {RCON{H_2}}\limits_{{\text{Amide}}} $$

Thereis no reaction hence the resultant mixture contains $$C{H_3}COO{C_2}{H_5} + NaCl.$$

\[KMn{{O}_{4}}\]   converts \[-C{{H}_{3}}\]  group of toluene into \[-COOH\]   while $$HI$$  reduces \[-COOH\]   group into \[-C{{H}_{3}}\]  group.

∴ acidity order is I > II > III > IV

Due to resonance in carboxylate ion, the double bond character of $$C=O$$  bond in carboxylic acids is greatly reduced as compared to that in aldehydes and ketones.

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