Since this process involves a matter-state change from solid to liquid, melting is occurring.
Ionic compounds have very strong intermolecular 'bonds': this is because it is formed by a metal atom donating one or more electrons to a non-metal atom in order to result in complete valence shells, with the effect that opposite ions are formed (opposites attract). Hence a large input of energy is needed to overcome these 'bonds' and form a liquid from the giant solid ionic lattice - therefore ionic compounds have high melting and boiling points.
Conversely a covalent bond occurs between two non-metal atoms - unlike ionic compounds which form giant ionic structures, covalent bonds are used to form molecules. These only have weak intermolecular forces, which need a small energy input to overcome: therefore the melting and boiling points will be much lower.
Considering that the compound has been taken from the freezer, which is 0 degrees celcius or lower, the state change has occurred at a low temperature. This makes it extremely likely that the compound is covalent.
In conclusion, the correct answer is d.