The missing structures `A` and `B` in the recation sequence:
`R -CH_(2)-CH_(2)OH overset(AI(2)O_(3))underset(350^(@)C)rarrR-CH=CH_(2)overset((i)O_(3))underset((ii)Zn//H_(3)O)rarr`
`RCHO +A, RCHO overset(Reduct)rarrB`, are

Options

A. `CH_(3) OH, RCOOH`
B. Methanal, RCHOHR
C. Ethanal, RCOOH
D. Methanal , `RCH_(2) OH`

Answer

To solve the problem, we need to identify the missing structures A and B in the reaction sequence involving an alcohol, its dehydration to form an alkene, and subsequent reactions leading to aldehydes and alcohols.

### Step-by-Step Solution:

1. **Identify the starting material:**
The starting material given is `R-CH2-CH2OH`, which is a primary alcohol.

2. **Dehydration of the alcohol:**
The first step involves the dehydration of the alcohol using `AI2O3` at `350°C`. This process removes a water molecule from the alcohol, resulting in the formation of an alkene. The alkene formed is `R-CH=CH2`.
- **Structure A:** `R-CH=CH2` (the alkene formed).

3. **Ozonolysis of the alkene:**
The alkene undergoes oxidative cleavage in the presence of ozone (O3) followed by reduction with zinc (Zn) and water (H2O). This reaction cleaves the double bond and forms ozonides, which are unstable and decompose to give carbonyl compounds.
- The ozonolysis of `R-CH=CH2` yields two products: `RCHO` (an aldehyde) and `HCHO` (formaldehyde).
- **Structure A:** `HCHO` (formaldehyde).

4. **Reduction of the aldehyde:**
The aldehyde `RCHO` undergoes reduction to form an alcohol. A common reducing agent for this reaction is lithium aluminum hydride (LiAlH4), which provides hydride ions (H-) to reduce the carbonyl group of the aldehyde.
- The reduction of `RCHO` leads to the formation of `R-CH2OH`.
- **Structure B:** `R-CH2OH` (the corresponding alcohol).

### Final Structures:
- **Structure A:** `HCHO` (formaldehyde).
- **Structure B:** `R-CH2OH` (the alcohol formed from the reduction of the aldehyde).

### Summary of Structures:
- A = HCHO (formaldehyde)
- B = R-CH2OH (the alcohol)