Compound P ($\mathrm{C}{}_6\mathrm{H}{}_{12}$) gives propanone and propanal on ozonolysis with reductive work-up. P is treated with (i) $\mathrm{BH}{}_3$ in THF, (ii) $\mathrm{H}{}_2\mathrm{O}{}_2/\mathrm{NaOH}$ to give Q, and Q is heated with concentrated $\mathrm{H}{}_2\mathrm{SO}{}_4$ to give R as the major alkene. R is

Propanone plus propanal means P is $(\mathrm{CH}{}_3){}_2\mathrm{C}=\mathrm{CH}-\mathrm{CH}{}_2\mathrm{CH}{}_3$, 2-methylpent-2-ene. Hydroboration-oxidation puts OH on the less substituted carbon C-3, giving 2-methylpentan-3-ol, $(\mathrm{CH}{}_3){}_2\mathrm{CH}-\mathrm{CH}(\mathrm{OH})-\mathrm{CH}{}_2\mathrm{CH}{}_3$. Acid dehydration follows Saytzeff's rule (and a hydride shift leads to the same tertiary cation), giving the trisubstituted alkene 2-methylpent-2-ene as the major product.