The correct order of acidity in given compounds
(i) `FCH_(2)COOH`
(ii) `CICH_(2)COOH`
(iii) `NO_(2) CH_(2)COOH`
(iv) `CH_(3)COOH`.

Options

A. `igt ii gt iii gt iv`
B. `iv gt iii gt ii gt i`
C. `iii gt iv gt igt ii`
D. `iii gt igt ii gt iv`.

Answer

To determine the correct order of acidity for the given compounds, we need to analyze the effects of the substituents on the carboxylic acid group (-COOH) in each compound. The compounds are:

1. `FCH2COOH` (Fluoroacetic acid)
2. `CICH2COOH` (Chloroacetic acid)
3. `NO2CH2COOH` (Nitroacetic acid)
4. `CH3COOH` (Acetic acid)

### Step-by-Step Solution:

**Step 1: Understand the effect of substituents on acidity.**
- Acidity in carboxylic acids is influenced by the ability of substituents to withdraw or donate electron density. Electron-withdrawing groups (EWGs) increase acidity by stabilizing the negative charge on the conjugate base (the carboxylate ion) after deprotonation.
- The order of electron-withdrawing ability is generally: Nitro (NO2) > Halogens (F, Cl) > Alkyl groups (like CH3).

**Step 2: Analyze each compound.**
- **`NO2CH2COOH`**: The nitro group is a strong electron-withdrawing group due to its -I (inductive) and -M (mesomeric) effects. This will significantly increase the acidity.

- **`FCH2COOH`**: The fluorine atom is also an electron-withdrawing group, but it is less effective than the nitro group. It has a -I effect, which will increase acidity, but not as much as NO2.

- **`CICH2COOH`**: Chlorine is another electron-withdrawing group, but it is less effective than fluorine. Therefore, it will have a lower acidity than both NO2 and F.

- **`CH3COOH`**: The methyl group (CH3) is an electron-donating group (+I effect), which decreases acidity as it increases electron density on the carboxylate ion, making it less stable.

**Step 3: Establish the order of acidity.**
Based on the analysis:
1. `NO2CH2COOH` (most acidic due to strong -I effect)
2. `FCH2COOH` (next most acidic due to -I effect)
3. `CICH2COOH` (less acidic than F due to weaker -I effect)
4. `CH3COOH` (least acidic due to +I effect)

Thus, the correct order of acidity is:
**NO2CH2COOH > FCH2COOH > CICH2COOH > CH3COOH**

### Final Answer:
The correct order of acidity is:
**(iii) `NO2CH2COOH` > (i) `FCH2COOH` > (ii) `CICH2COOH` > (iv) `CH3COOH`**