Question

how does the melting point of a substance indicate the strength of its intermolecular force of attraction​

Answer 1

The molecules are held together by intermolecular force of attraction. More the force the fusion takes after some time only that means the melting point is high. So molecules with greater molecular forces have high melting point and less molecular forces have low melting point.

Answer 2

On heating a solid, the kinetic energy of the particle increases. The particle start vibrating with greater speed. The energy supplies by heat overcomes the force of attraction between the particles.

If this force of attraction is more, then more heat energy will be necessary to overcome this force. So, the melting point of the solid will be higher.