Ally chloride on dehydrochlorination gives

propadiene

The correct answer is option 1. propadiene.

Ally chloride (3-chloropropene) on dehydrochlorination gives propadiene (also known as allene).

The reaction proceeds through an E₂ elimination reaction, which means that two atoms or groups are eliminated from the same molecule in a concerted reaction. In this case, the two atoms that are eliminated are chlorine and hydrogen.

The reaction is illustrated below:

\(CH_2=CHCH_2Cl \rightarrow CH_2=C=CH_2 + HCl\)

Propadiene is a colorless gas with a strong odor. It is used as a starting material for the synthesis of other compounds, such as 1,3-butadiene and acrolein.

The other options are incorrect.

Option (2), propylene, is not formed because the dehydrochlorination reaction does not produce a double bond.

Option (3), allyl alcohol, is not formed because the dehydrochlorination reaction does not produce an alcohol group.

Option (4), acetone, is not formed because the dehydrochlorination reaction does not produce a ketone group.