Question

Question #2db1c

Answer 1

but-1-ene: `CH_2=C(H)-CH_2-CH_3`
but-2-ene: `CH_3 - C(H) = C(H) - CH_3`

When you add chlorine to an alkene it undergoes an addition reaction to form a haloalkane. The double bond is broken and the Cl's go on to these new bonds.
But-1-ene + `Cl_2` can form 1,2-dichlorobutane
But-2-ene + `Cl_2` can form 2,3-dichlorobutane

These are different because of where the double bond is in the molecules. The Cl groups go onto the spare space on the C atom that previously was double bonded.