Which of the following molecules is aromatic?

• A. $C_5{H}_8$ (cyclopentadiene)
• B. $C_4{H}_8$ (cyclobutane)
• C. $C_6{H}_{12}$ (cyclohexane)
• D. $C_6{H}_6$ (benzene)

Answer: (D)

Verified step by step guidance

1. Recall the criteria for aromaticity: a molecule must be cyclic, planar, fully conjugated (p orbitals at every atom in the ring), and follow Hückel's rule, which states it must have (4n + 2) π electrons, where n is a non-negative integer.
2. Examine each molecule to determine if it meets these criteria. For example, check if the ring is planar and if there are continuous overlapping p orbitals allowing for conjugation.
3. Count the number of π electrons in each molecule. Double bonds contribute 2 π electrons each, and lone pairs or negative charges can also contribute if they are part of the conjugated system.
4. Apply Hückel's rule by plugging the number of π electrons into the formula (4n + 2). If the number fits this formula for some integer n, the molecule is aromatic.
5. Identify benzene (C\_6H\_6) as the molecule that meets all these criteria: it is cyclic, planar, fully conjugated with 6 π electrons, and satisfies Hückel's rule with n=1, making it aromatic.