`RCH=CH_(2)` can be obtained by `:`

Options

A. `R-overset(O)overset(||)(C)H` and `(C_(6)H_(5)) P = CH_(2)`
B. By heating `RCH_(2)CH_(2) underset(O)underset(darr)(N)(CH_(3))_(2)`
C. By heating` RCH_(2)CH_(2)OCOCH_(3)`
D. All of these

Explanation

To determine how the compound \( RCH=CH_2 \) can be obtained, we can analyze the options provided in the question and the reactions involved. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Compound
The compound \( RCH=CH_2 \) is an alkene, specifically an unsubstituted alkene where \( R \) can be any alkyl group.

### Step 2: Analyze the Reaction Options
We need to consider the different reactions that can lead to the formation of this alkene. The options provided include reactions involving carbonyl compounds, amine oxides, and esters.

### Step 3: Wittig Reaction
1. **Wittig Reaction**: This reaction involves the reaction of a carbonyl compound with a phosphonium ylide (phosphorous-alite).
- The carbonyl compound has a carbon atom that is electrophilic due to the presence of the electronegative oxygen.
- The phosphonium ylide acts as a nucleophile.
- When they react, they form a betaine complex, which eventually leads to the formation of the alkene \( RCH=CH_2 \).

### Step 4: Copper Elimination Reaction
2. **Copper Elimination Reaction**: This reaction involves N-oxide compounds.
- When heated, the N-oxide can undergo elimination to form an alkene.
- The reaction involves the nucleophilic attack of the negative charge on oxygen on a hydrogen atom, leading to the formation of the alkene \( RCH=CH_2 \).

### Step 5: Ester Dehydration
3. **Ester Dehydration**: Heating an ester can also lead to the formation of alkenes.
- The ester can undergo elimination reactions when heated, leading to the formation of an alkene and an alcohol.

### Step 6: Conclusion
Since all three reactions (Wittig reaction, copper elimination reaction, and ester dehydration) can lead to the formation of the alkene \( RCH=CH_2 \), the correct answer is that \( RCH=CH_2 \) can be obtained from all of the mentioned reactions.

### Final Answer
Thus, the correct option is:
**D. All of these**

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