The decreasing order of reactivity towards nucleophilic acyl substitution is
`{:((i),CH_(3)COCl,(ii),CH_(3)COOC_(2)H_(5)),((iii),CH_(3)CONH_(2),(iv),(CH_(3)CO)_(2)O):}`

Options

A. `(i) gt (iv) gt (iii) gt (ii)`
B. `(i) gt (iv) gt (ii) gt (iii)`
C. `(iv) gt (iii) gt (i) gt (ii)`
D. `(iii) gt (i) gt (iv) gt (ii)`

Explanation

To determine the decreasing order of reactivity towards nucleophilic acyl substitution for the given compounds:

1. **Identify the compounds:**
- (i) CH₃COCl (Acyl chloride)
- (ii) CH₃COOC₂H₅ (Ester)
- (iii) CH₃CONH₂ (Amide)
- (iv) (CH₃CO)₂O (Anhydride)

2. **Understand the reactivity order:**
The general order of reactivity for acyl compounds in nucleophilic acyl substitution is as follows:
- Acyl chlorides > Anhydrides > Esters > Amides

3. **Rank the given compounds based on the reactivity:**
- **Acyl Chloride (i)**: CH₃COCl is the most reactive due to the presence of chlorine, which is a good leaving group.
- **Anhydride (iv)**: (CH₃CO)₂O is next in reactivity. The leaving group here is also a good one, making it more reactive than esters and amides.
- **Ester (ii)**: CH₃COOC₂H₅ is less reactive than anhydrides and acyl chlorides due to the presence of the alkoxy group (OC₂H₅), which is a poorer leaving group.
- **Amide (iii)**: CH₃CONH₂ is the least reactive because the nitrogen atom can stabilize the carbonyl group through resonance, making it harder for the nucleophile to attack.

4. **Final order of reactivity:**
Based on the above analysis, the decreasing order of reactivity towards nucleophilic acyl substitution is:
- (i) CH₃COCl > (iv) (CH₃CO)₂O > (ii) CH₃COOC₂H₅ > (iii) CH₃CONH₂

Thus, the final answer is:
**(i) > (iv) > (ii) > (iii)**