A is an alkene. A contains (i) 3 C – C σ-bonds, (ii) 8 C – H σ-bonds and (iii) 1 C – C π bond. (A) $\xrightarrow{\mathrm{O}_3}$ 2RCHO Molar mass of RCHO = 44u (i) The clue to finding the structure and therefore the IUPAC name of A lies in the aldehyde RCHO. The mass of – CHO group is 29 u. This implies that the alkyl group attached has a mass of 44 – 29 = 15. This can be the mass of –CH3 group only. ∴ RCHO is $\mathrm{CH_3CHO}$. (ii) Since 2 moles of only CH3CHO is obtained. Therefore, the alkene is $\mathrm{H}_3\mathrm{C}-\underset{\mathrm{H}}{\underset{\vert}{\mathrm{C}}}=\mathrm{O}$ + $\mathrm{O}=\underset{\mathrm{H}}{\underset{\vert}{\mathrm{C}}}-\mathrm{CH}_3$ → $\underset{\text{2-Butene}}{\mathrm{H_3C-HC=CH-CH_3}}$ Thus, (A) is $\mathrm{CH_3-HC=CH-CH_3}$ and its IUPAC name is but-2-ene. This structure also confirms the given number of σ and π bonds.