Highest enol content will be shown by:

Keto-Enol Tautomerism:

The enol content of a carbonyl compound depends on the stability of the enol form. Factors that stabilize the enol form include:

1. Conjugation with other double bonds
2. Intramolecular hydrogen bonding
3. Aromaticity (if applicable)

Analysis of Options:

(a) Cyclohexane-1,3-dione: The two carbonyl groups are separated by one CH₂ group, so the enol form has extended conjugation and hydrogen bonding making enol form particularly stable.

(b) Cyclohexane-1,3,5-trione: This compound has three carbonyl groups alternating with CH₂ groups. The enol form is aromatic and has maximum conjugation and multiple intramolecular hydrogen bonds, making it the most stable enol form. Aromaticity alone is the biggest differentiator here.

(c) Cyclohexane-1,4-dione: Has two carbonyl groups with two CH₂ groups between them. The enol form has no conjugation and no hydrogen bonding due to both carbonyl groups positioned diagonally across.

(d) Cyclohexane-1,2,3-trione: Three adjacent carbonyl groups. The middle carbonyl group can't participate in tautomerism. Also three carbonyl groups repel each other strongly due to being on same side. The enol form has limited stabilization.

Conclusion: Cyclohexane-1,3,5-trione (option b) shows the highest enol content due to maximum stabilization through aromaticity and multiple intramolecular hydrogen bonding sites.

$\boxed{\text{Answer: (b)}}$