Looking at liquid-gas equilibria, then sure, the vapor pressure of the liquid would be higher than it's corresponding gas vapor above it at the boiling point and vice versa-but you cannot just read this and copy and paste the phrase and replace the wording to say "Above the melting point, the vapor pressure of the
solid will be greater than that of the
liquid" and vice versa.
The book's statement is correct as is, and although it might not be directly relevant to more general MCAT discussions, it does seem counter-intuitive at first. It would be helpful to think in terms of IMFs (as suggested in another post), and the thermal energy brought about by changes in temperature that is varied to form them or disrupt them-but this will not get you very far. Generally speaking, at a given pressure, the vapor pressure of a liquid is is greater than a solid. This makes sense, in that a solid is a more condensed phase, and the atoms & molecules within it have far less capacity (available energy) to move around and escape the lattice into the liquid or gas phases. Note that there are exceptions to what I'm saying, lets simplify things by just assuming we're talking about water (H2O) from here on out.
The question your asking is in terms of above or below the melting point; pressure is not specified, and we are in essence looking at vapor pressures at given temperatures. Vapor pressure is between whatever phase (liquid or gas) you're referring to and it's vapor (gas) phase. I think you're getting mixed up in liquid/gas phase equilibria. The key here is we are talking about the solid-vapor as well as the liquid-gas equilibria, and not somehow talking only about the solid-liquid boundary, which would be weird because both of those aren't vapors at all.
above the melting point, shouldn't the solid vapor pressure be greater than the liquid since the solid will be melting?
No. The solid is
above the melting point-if we are looking at water, the melting point is the flat portion of the curve where the temperature is changing, and all of the energy is going into breaking the intermolecular bonds associated with the lattice. If we are above this point, then all of these bonds have been broken, and the solid is now a liquid and no longer melting-any energy that is inputted to it is now simply raising the temperature. Therefore little, if any, solid will exist above the melting point, and therefore will not be contributing much to the vapor pressure at all! The liquid, however, will be the dominant phase above the melting point and be the dominant contributor to the vapor pressure.
'above the melting point, liquid vapor pressure is greater than that of the solid ; below the melting point the liquid vapor pressure is less than that of the solid'
Therefore, this statement is correct. The opposite is also true by the same qualitative reasoning. As I pointed out earlier, the most confusing part is perhaps mistakenly trying to cram the "vapor" part of this into the solid-liquid phase change itself (copy and pasting). The quantitative side of this is buried underneath things like the Clausius-Clapeyron eqn, which you need not to get into, especially if this is in the context of MCAT prep. I'll admit this type of question was a bit of a pothole for me as well as I was rolling through the book.
