An alkene on ozonolysis gives methanal as one of the products. Its structure is:

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Accepted Answer

1. **Principle of Ozonolysis:** Ozonolysis is a reaction used to locate the position of a double bond in an alkene. It involves the addition of ozone ($O_3$) to the carbon-carbon double bond to form an ozonide intermediate, which is then cleaved by zinc and water ($Zn/H_2O$) to yield smaller carbonyl compounds (aldehydes or ketones) [NCERT 11th, Unit 9, Sec 9.3.5].
2. **Analysis of Products:** The question states that **methanal** (formaldehyde, $HCHO$) is one of the products. Methanal is a one-carbon aldehyde. For an alkene to produce methanal upon cleavage of the double bond, the double bond must be situated at the end of the carbon chain, specifically involving a terminal methylene group ($=CH_2$).
3. **General Reaction:** 
   $$ R-CH=CH_2 + O_3 \xrightarrow{Zn/H_2O} R-CHO + HCHO $$
4. **Conclusion:** While the specific chemical structures for the options are not visible in the text, the correct answer (Option 2) must be an alkene possessing a terminal $=CH_2$ group (e.g., a terminal alkene or a methylene derivative of a cyclic compound).

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