Dehydration of alcohols to alkenes is catalysed by acids like concentrated sulphuric acid.

1. Mechanism: The reaction typically proceeds via an E1 mechanism involving the formation of a carbocation intermediate .
2. Carbocation Stability: The stability of carbocations follows the order: Tertiary ($3^{\circ}$) > Secondary ($2^{\circ}$) > Primary ($1^{\circ}$) . Less stable carbocations can rearrange (via 1,2-hydride or 1,2-methyl shifts) to form more stable carbocations.
3. Product Formation: The final step involves the elimination of a proton ($H^+$) from a $\beta$-carbon. According to Zaitsev's rule (also Saytzeff), the major product is the most highly substituted alkene (the one with the greater number of alkyl groups attached to the doubly bonded carbon atoms) due to stability from hyperconjugation .

Any alkene that cannot be formed via the elimination of a proton from the initial or rearranged carbocation would be the correct answer for 'not a product'.