Pentane and neopentane have the same formula $C_5H_{12}$ and the same molar mass, yet pentane boils at 36 °C and neopentane at 9.5 °C. What accounts for the 26-degree gap?

B. Pentane is a long chain with more contact surface

Boiling breaks intermolecular forces, not bonds, so the covalent option is off the point and the masses are identical. Both molecules are nonpolar, leaving dispersion, which grows with contact area, a chain can lie alongside its neighbours and a sphere touches at a point. This is why branching lowers boiling points right across organic chemistry.