The type of isomerism present in the pair of compounds but-1-ene and but-2-ene is positional isomerism. Positional isomers are constitutional isomers that have the same molecular formula but differ in the position of the functional group or substituent on the parent chain.But-1-ene has the double bond between the first and second carbon atoms CH2=CH-CH2-CH3 , while but-2-ene has the double bond between the second and third carbon atoms CH3-CH=CH-CH3 .The difference in the position of the double bond leads to some differences in their chemical and physical properties:1. Chemical properties:- Electrophilic addition reactions: Both but-1-ene and but-2-ene undergo electrophilic addition reactions, but the products formed may be different due to the position of the double bond. For example, when reacting with hydrogen bromide HBr , but-1-ene forms 1-bromobutane, while but-2-ene forms 2-bromobutane.- Polymerization: Both but-1-ene and but-2-ene can undergo polymerization, but the resulting polymers will have different structures due to the position of the double bond in the monomers.2. Physical properties:- Boiling point: The boiling points of but-1-ene and but-2-ene are quite similar but-1-ene: -6.3C, but-2-ene: -3.7C because they have the same molecular formula and similar molecular weights. However, the slight difference in boiling points can be attributed to the difference in the position of the double bond, which may affect the overall shape and symmetry of the molecules, leading to slightly different intermolecular forces.- Density: The densities of but-1-ene and but-2-ene are also quite similar but-1-ene: 0.62 g/mL, but-2-ene: 0.64 g/mL for the same reasons mentioned above.In summary, but-1-ene and but-2-ene exhibit positional isomerism, and while their chemical and physical properties are quite similar, the differences can be attributed to the position of the double bond in the molecules.