Question

why does cis-2-butene have high bp than trans-2-butene ?

Answer 1

In cis-2-butene 2 methyl group falls into vander Waals repulsive force that's why it has higher bp than trans-2-butene where 2 methyl groups are in opposite side

Answer 2

Greater the surface area higher the boiling point due to vanderwalls force is directly proprioception to surface area