Assertion A: Enol form of acetone [$$CH_3COCH_3$$] exists in < 0.1% quantity. However, the enol form of acetyl acetone  [$$CH_3COCH_2OCCH_3$$] exists in approximately 15% quantity.
Reason R: enol form of acetyl acetone is stabilized by intramolecular hydrogen bonding, which is not possible in enol form of acetone.
Choose the correct statement:

$$10^{-5}\%$$) because the keto form with its strong $$C=O$$ bond is significantly more thermodynamically stable than the enol form with a

$$C=C$$ bond. However, in $$\beta$$-diketones like acetylacetone ($$CH_3COCH_2COCH_3$$), the enol form exists in a very significant quantity (varying heavily by solvent, often 15% in aqueous solutions and up to 76% in non-polar liquid states). Therefore, the assertion is True.

1. Intramolecular Hydrogen Bonding: The hydrogen atom of the newly formed $$-OH$$ group gets attracted to the oxygen of the remaining $$C=O$$ group. This forms a highly stable, 6-membered chelate ring.
2. Conjugation: The newly formed $$C=C$$ double bond is now in conjugation with the adjacent $$C=O$$ double bond, providing extra resonance stability.

   Because standard acetone only has one oxygen atom, it cannot form an intramolecular hydrogen bond, nor can it achieve this extended conjugation. Therefore, the reason is True.

The primary reason why acetylacetone has such a vastly higher enol content compared to acetone is precisely because of the stabilization provided by that intramolecular hydrogen bond (and conjugation). Therefore, the Reason perfectly explains the Assertion.