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JAMB Physics 2020 Paper

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Question : 33

Total: 38

In an experiment in which molten naphthalene is allowed to cool, the cooling curve i n the figure was obtained. The temperature 80 $^o$ C is known as the

cooling temperature
boiling point
melting point
vaporization point

Solution:

Concept:

During cooling, a pure substance shows a constant temperature while changing from liquid to solid; this is the freezing point, which equals the melting point.

Explanation:

Molten naphthalene cools, and at

80^\circ\mathrm{C}

the temperature remains steady while solid is forming.

This constant temperature is the freezing point of naphthalene.

Since freezing point and melting point are the same for a pure substance,

80^\circ\mathrm{C}

is its melting point.

Answer:

C. melting point

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