Can anyone help me with chemistry?

Question

Why does the boiling point of a liquid vary with pressure while the melting point of a solid does not?

Answer 1

During boiling a portion of a liquid becomes a vapor.  The vapor molecules have more kinetic energy (of motion) than liquid molecules which is why they can exert increased pressure on the entire closed container and liquid surface.  The pressure on a square inch of container surface depends upon the number of moving vapor molecules that bounce off of it and the velocity of the molecules.

When a solid melts its molecules vibrate from added heat energy that breaks the bonds allowing the molecules to flow as a liquid.  That does not result in more pressure on the container because the volume changes very little (unlike a vapor).