Final answer:
The unknown compound's properties of being soft, low melting point, non-conductive, and insoluble in water with floating characteristic, suggest that it has covalent molecular bonds.
Step-by-step explanation:
The macroscopic properties you've described for the unknown solid suggest that it exhibits a type of bonding that confers certain physical characteristics. The fact that the solid is soft and can be cut with a knife, melts at relatively low temperature (35°C), and does not dissolve in water but instead floats on the surface are all indicative of a compound with covalent molecular bonds.
Covalent molecular compounds are comprised of molecules held together by relatively weak intermolecular forces, which account for the low melting points. The inability to conduct electricity rules out ionic and metallic bonds, as ionic compounds conduct electricity when molten or in solution, and metallic substances can conduct electricity due to delocalized electrons. The low melting point and the poor solubility in water also support the idea that the substance is not ionic, as ionic compounds usually have high melting points and most are soluble in water. Since the solid floats on water, it is likely less dense than water, which is also a characteristic more common to molecular solids than to solids with other types of bonding.