Al₂(CO₃)₃ would have the highest melting point.
If it existed, it would consist of Al³⁺ and CO₃²⁻ ions, and the strong attraction between them would give the ionic compound a high melting point.
C₁₂H₂₂O₁₁ and C₈H₁₆ are organic compounds (molecular). Molecular compounds typically have low melting points.
Water, of course, freezes at 0 °C.
