Dehydration of menthol forms an alkene via E1 mechanism Steps:

• Protonate the hydroxyl group of menthol with H2SO4 to form a good leaving group.
• Loss of water from the secondary alcohol yields a secondary carbocation at the carbon originally bearing the OH.
• The carbocation undergoes deprotonation from an adjacent carbon, following Zaitsev's rule to favor the more substituted alkene.
• The major product is the trisubstituted alkene with the double bond between carbons 1 and 2 in the menthol numbering.

Why D is correct:

• D shows the trisubstituted cyclohexene with isopropyl at C3 and methyl at C6, matching Zaitsev's rule for the most stable alkene from menthol dehydration.

Why the others are wrong:

• A: Depicts a disubstituted alkene, less stable and minor product.
• B: Shows incorrect double bond position, violating elimination from the carbocation site.
• C: Represents an unrearranged primary alkene, thermodynamically unfavorable.

Final answer: D