How many H atoms will be replaced by D–atoms :

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To find the number of hydrogen atoms replaced by deuterium (D) atoms when the given compound is treated with excess OD⁻/D₂O, we look for all the acidic hydrogens ( $α$ -hydrogens) that can form a stable, resonance-stabilized enolate ion:

$α^{'}$ -Position (C₆): The sp³ carbon adjacent to the carbonyl group on the right side (CH₂ group) contains 2 acidic hydrogens that readily exchange with deuterium.

$α$ -Methyl Position (C₂-CH₃): The methyl group attached to the $α$ -carbon of the double bond has 3 acidic hydrogens because its deprotonation forms a highly stable, conjugated dienolate system (CH₂=C-C=C-O⁻).

Other Positions: The C₄ carbon is quaternary (has two methyl groups and no hydrogens), and the C₃-methyl and C₅ hydrogens cannot form a conjugated enolate system.

Total H-atoms replaced = $2 (a t C_{6}) + 3 (a t C_{2} - C H_{3}) = 5.00$

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