Which is more soluble in water, 3-bromocyclopropene or bromocyclopropane?

The tendency of a compound to do reaction with a solvent to form a solution is called solubility.

Here in this case, solubility of those compounds means the reaction between water as solvent and those compound as solute. The more is the reaction between solute and solvent, the more will be he solubility of those compounds.

Both the compounds reacts with H₂O to form the following compounds,

Now in case of the 1^st one, reaction with H₂O produces a cyclopropane cation which is aromatic in nature (from Huckel’s rule of (4n+2) π electrons, where n=0) where the 2^nd product is not as stable as the 1^st one as it is not aromatic. So, as a matter of fact, due to the high product stability in the 1^st one, the solubility of the 1^st compounds increases more than the 2^nd one.

So, 3-bromocyclopropene will be more soluble than bromocyclopropane.