The given reaction involves a process called decarboxylation, which is a common reaction for beta-keto esters. In this reaction, the beta-keto ester undergoes heating to lose carbon dioxide (CO₂), leading to the formation of an enol, which can tautomerize to a more stable keto form.

1. Identify the beta-keto ester: The compound provided is an ethyl ester with a carbonyl group two carbon atoms away from an ethoxy group (alkene). This structure is characteristic of beta-keto esters.

2. Mechanism of decarboxylation:

   • Heat causes the formation of an enolate ion as the beta-keto ester loses CO₂.
   • The enolate tautomerizes to form a more stable ketone.

   

3. Predict the product structure:

   • The remaining structure after CO₂ loss will correspond to a pentane derivative with a methyl side chain.
   • This matches the structure given in the correct option provided as the answer.

Therefore, the major product [X] formed is the ketone as depicted in the option with data-src-id "69879ec44ff7d55a3b543bf9".

Conclusion: The decarboxylation of the given beta-keto ester leads to the formation of a ketone product, which is the most stable form after the reaction.