Final answer:
The fatty acid with the highest melting point is A. 20 carbon chain with no double bonds, as it is the longest saturated chain which allows for tighter packing and stronger intermolecular forces.
Step-by-step explanation:
Understanding Fatty Acid Melting Points
The melting point of fatty acids is influenced by two main factors: the length of the carbon chain and the degree of saturation. Saturated fatty acids, which have no double bonds, tend to have higher melting points because their straight chains can pack tightly together, increasing the London dispersion forces between the molecules. In comparison, unsaturated fatty acids with one or more double bonds have kinks in their chains which prevent tight packing and result in lower melting points. With this in mind, we can conclude that among the given options, A. 20 carbon chain with no double bonds will have the highest melting point because it has the longest carbon chain with full saturation, while allowing for the maximum dispersion forces among molecules.