Which rule is followed when an unsymmetrical alkene undergoes acid hydrolysis (i.e. addition of unsymmetrical reagents)?

Markovnikov's Rule

The correct answer is option 3. Markovnikov's Rule.

When an unsymmetrical alkene undergoes acid hydrolysis (addition of water), Markovnikov's rule is followed.

Markovnikov's Rule: This rule states that in the addition of an unsymmetrical hydrogen halide (HX) to an unsymmetrical alkene, the hydrogen atom (H) from the HX molecule adds to the doubly bonded carbon atom that already has the greater number of hydrogen atoms, and the halogen (X) adds to the other carbon atom.

Acid Hydrolysis: In this context, acid hydrolysis refers to the addition of water (H₂O) to the alkene double bond, which is catalyzed by an acid. Even though water itself is symmetrical (H-O-H), during the reaction, the H⁺ from the acid combines with the oxygen, making the remaining OH act as the nucleophile attacking the alkene.

Markovnikov's rule applicability: Despite water being symmetrical, the mechanism of acid hydrolysis follows Markovnikov's rule because the carbon-oxygen bond in water is more polar than the O-H bond. The partially negative oxygen of the water molecule acts as the nucleophile that attacks the alkene, and the proton adds to the other carbon.

Other options:

Saytzeff's rule: This rule applies to elimination reactions, not addition reactions like acid hydrolysis.

Hoffmann rule: This is a less general rule used to predict the product of elimination reactions involving quaternary ammonium salts.

Markovnikov's rule is the most widely applicable rule to predict the regioselectivity (direction of addition) in the acid-catalyzed addition of water to unsymmetrical alkenes.