The major product of the following reaction is:

Step 1: Identify the starting material

The starting material is a diene, treated with an acid catalyst (like $\ce{H2SO4}$ or $\ce{HCl}$) that promotes cyclization.

Step 2: Identify the reaction type

For a diene with an appropriate geometry, intramolecular reaction via protonation gives a cyclic product through:

1. Protonation of one double bond → carbocation
2. Intramolecular attack by the other double bond
3. Ring closure → cyclic product Answer: Option (b)

Key Points to Remember:

• Intramolecular electrophilic addition of dienes favors 5- or 6-membered ring formation
• Proton-catalyzed cyclization follows Markovnikov's rule at each step
• Ring closure is kinetically favored for 5- and 6-membered rings (Baldwin's rules)