A carbonyl compound A(C₄H₈O), which undergoes haloform reaction gives compound B on reduction. B on heating with sulphuric acid gives a compound C which forms a mono-ozonide D. D on hydrolysis in present of zinc dust gives only acetaldehyde E. 

While converting from B to C, H₂SO₄ is used as a catalyst. What is the role of H₂SO₄ in this reaction?

Dehydrating agent

The correct answer is option 1. Dehydrating agent

Since carbonyl compound A(C₄H₈O) undergoes a haloform reaction, it must contain the group CH₃CO. Therefore, it is a ketone and must be biutan-2-one.

Since ketone A, i.e., butan-2-one gives compound B on reduction, therefore B must be 2-butanol.

Since B, i.e., 2-Butanol on heating with H₂SO₄ gives compound C which forms a mono-ozonide, therefore compound C must be an alkene.

Since alkene C forms a mono-ozonide D which on hydrolysis in presence of zinc dust (i.e., reductive ozonolysis) gives only acetaldehyde E, therefore, C must be symmetrical alkene , i.e., 2-Butene.

All  the reactions involved are: