Explain b.p. & m.p. of cis/trans-2-butene

trans-isomer have a more regular and symmetrical structure due to two bulky groups on opposite site each other. It can be packed more commpactly than cis-isomer in its solid state. Thus, Stronger the intermolecular foorces between trans-isomer.

Melting point involves the breaking of intermolecular forces, trans-isomer therefore has Higher melting point.

Both Two CH3 electron releasing groups at one side of cis-isomer , the molecule exerts net dipole moment. As a result, there is addition of dipole-dipole attraction force between cis-isomers.
However trans-isomer has no net dipole moment, since two dipole moment cancel out each other. Only weaker induced dipole - induced dipole attraction among
trans-isomers.
Thus, vaporizing trans-isomer with less energy, and lower boiling point is the trans-isomer.