Which of the following statements is true? a. the melting and freezing points of a substance are the same. b. the melting and boiling points of a substance are the same. c. the freezing and boiling points of a substance are the same. d. the heat of fusion and the heat of vaporization for a substance are the same.

The answer is A. The melting and freezing points of a substance are the same. The only difference between melting and freezing is the order in which they occur. Melting starts with a solid and changes into a liquid. Freezing starts with a liquid and changes into a solid. Think of water. At 0 degrees celsius and if the temperature was decreasing before, it would freeze. At 0 degrees celsius and the temperature was increasing before, it would melt. Look at a heating/cooling curve, the straight lines are the transition points. On a heating curve, the first straight line is for melting. On a cooling curve, the last straight line is for freezing. They both occur at the same temperature.

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a. they are both space stations

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