The compound that will react most readily with gaseous bromine has the formula is: C4H10, C2H4, C3H6, C2H2

The compound that will react most readily with gaseous bromine has the formula C3H6. This is because C3H6 (propene) is an alkene, meaning it contains a carbon-carbon double bond. Alkenes readily undergo addition reactions with bromine, where the bromine molecule adds across the double bond. The other compounds listed are alkanes (C4H10, saturated hydrocarbons with only single bonds) or alkynes (C2H2, containing a carbon-carbon triple bond). Alkanes are relatively unreactive compared to alkenes, and although alkynes can also react with bromine, they generally react less readily than alkenes.