Question

alkanes with odd number of carbons have lower melting point than those with an even number of carbon atom

Answer 1

This is because even numbered alkanes pack well in the solid phase, forming a well-organized structure, which requires more energy to break apart. The odd-numbered alkanes pack less well and so the "looser" organized solid packing structure requires less energy to break apart

See the pic and also the sawtooth like trend in alkanes melting point.
Thanks.
Tripathy