The two possible enantiomers for the starting material and the products are shown below,
Where;
J = (S)-1,4-dimethylcyclobut-1-ene
Or,
J = (R)-1,4-dimethylcyclobut-1-ene
And,
K = 1,2-dimethylcyclobutane
Both enantiomers have same molecular formula (C₆H₁₀) but different stereochemistry about chiral carbon.
Upon catalytic hydrogenation two hydrogen atoms are added across double bond resulting in the formation of cyclobutane.