Q.But-1-ene is treated with dilute $\text{H}_2\text{SO}_4$/$\text{H}_2\text{O}$. Give the structure of the major alcohol formed and name the mechanism/rule that decides which alcohol is major.

But-1-ene, $\text{CH}_2{=}\text{CHCH}_2\text{CH}_3$, protonates at C-1 (the terminal carbon, which already carries two hydrogens) because this generates the more stable secondary carbocation at C-2, rather than a primary carbocation at C-1. Water then attacks this secondary carbocation at C-2, and loss of a proton gives the alcohol: $\text{H}^+$ effectively adds to C-1 and $-\text{OH}$ to C-2, exactly as Markovnikov's rule predicts (the electrophile's H goes to the carbon already bearing more hydrogens).

Identify which of the two possible carbocations (protonating at C-1 vs C-2) is more stable, then place OH on that carbon.

Adding OH to the terminal carbon (anti-Markovnikov) by mistake, which is instead the outcome of the separate hydroboration-oxidation route, not acid-catalysed hydration.