You have two $C_6{H}_{10}O$  ketones, I and II. Both are optically active, but I is racemized by treatment with acid and II is not. Wolff kishner reduction of both ketones gives the same achiral hydrocarbon, formula $C_6{H}_{12}$ .  What reasonable structures may be assigned to I and II respectively?

The reasonable structures assigned to ketones I and II, given your data and images, are:

Structure I

• Name: 2-Methylcyclopentanone
• Structure: Methyl group at the chiral carbon (C-2) of cyclopentanone.
• Feature: Optically active, but racemizes with acid (due to enolization at the α-position to the carbonyl). The ability to form enantiomers (chiral) and undergo acid-catalyzed racemization is due to the exchange of H across the chiral center via enol formation.

Structure II

• Name: 3-Methylcyclopentanone
• Structure: Methyl group at C-3 of cyclopentanone (also chiral), but no α-H at the chiral center, so enolization at this center cannot occur.
• Feature: Optically active, but does not racemize under acid, as enolization cannot occur at the chiral center. Hence, configuration is retained under acidic conditions.

Both Ketones Yield the Same Hydrocarbon

• Wolff-Kishner reduction of both ketones produces methylcyclopentane (C6H12), which is achiral, indicating both structures are isomeric methylcyclopentanones.

Conclusion:

• Ketone I is 2-methylcyclopentanone (racemizes by acid).
• Ketone II is 3-methylcyclopentanone (does not racemize under acid).
• Both reduce to methylcyclopentane. Here are the reasonable structures for the two ketones described:

Structure I: 2-Methylcyclopentanone

• Structure: Methyl group attached to the chiral center (C-2) of cyclopentanone.
• Properties: It is chiral and can racemize under acidic conditions by enolization. The images show that the methyl group at position 2 makes the center chiral, and proton exchange can generate both enantiomers (optical activity lost by racemization).

Structure II: 3-Methylcyclopentanone

• Structure: Methyl group attached to the 3-position of cyclopentanone (also chiral).
• Properties: This compound is chiral but does NOT racemize under acidic conditions, as the chiral carbon (with the methyl substituent) does not have an α-hydrogen to enolize; thus, the stereochemistry remains unchanged in acid as shown in the image.

Wolff Kishner Reduction:

Both ketones can be reduced to methylcyclopentane (C₆H₁₂), which is achiral.

Summary:

• I = 2-methylcyclopentanone (chiral, racemizes in acid)
• II = 3-methylcyclopentanone (chiral, does not racemize in acid)
• Both yield methylcyclopentane (C₆H₁₂) after Wolff Kishner reduction.

This assignment is supported by the structures and mechanistic explanations shown in the images, meeting all conditions stated in the question