And for a given substance occur at the same temperature.
a. melting, freezing
b. melting, boiling
c. freezing, evaporation
d. boiling, freezing

Melting and freezing for a given substance occurs at the same temperature. Because the temperature at which the solid starts to melt is also the temperature at which the liquid starts to freeze. They are at chemical equilibrium.

in chemistry, a solution’s concentration is how much of a dissolvable substance, known as a solute, is mixed with another substance, called the solvent. the standard formula is c = m/v, where c is the concentration, m is the mass of the solute dissolved, and v is the total volume