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Question:

In the reaction sequence, the product B is: 2CH3CHO + OH⁻ → A Δ → B

CH3−CH=CH−CHO

CH3−CH2−CH2−CH2−OH

CH3−CH2−CH2−CH3

CH3COCH3

Solution:

In the reaction sequence, 2CH3CHO + OH⁻ → A Δ → B; the product B is CH3−CH=CH−CHO.
2CH3CHO + OH⁻ → CH3−CH(OH)CH2−CHO (A)
Δ → CH3−CH=CH−CHO (B)
In presence of hydroxide ions, two moles of acetaldehyde condense to form beta-hydroxy alcohol (compound A) which on dehydration forms alpha beta-unsaturated aldehyde (compound B). Thus option (A) is correct.