Answer:
Diamonds
Step-by-step explanation:
The melting point of sugar is 186C
The melting point of oxygen is -218C
The melting point of diamonds are 4078C
Therefore diamonds have the highest melting point.
You can also think of their structures, as diamonds have a covalent network structure, meaning they are really strong and have a high melting point
Oxygen has a covalent molecular structure
Sugar has a much weaker covalent network structure