Answer: The given temperature is known as melting point of naphthalene.
Step-by-step explanation:
Melting point is defined as the temperature at which solid gets converted to liquid.
The temperature remains constant until all the solid has been converted to liquid. At this temperature, solid state and liquid state are present at equilibrium.

We are given:
A solid piece of naphthalene is heated till 80°C until all the solid is melted.
Hence, the given temperature is known as melting point of naphthalene.