Final answer:
To determine the heat of fusion for substance 'X', divide the total energy required (4000 J) by the mass (8.00 g), resulting in a heat of fusion of 500 J/g; thus, option b (500 J/g) is correct.
Step-by-step explanation:
The student's question pertains to finding the heat of fusion of a substance 'X'. To calculate the heat of fusion, one uses the amount of heat energy needed to melt a certain mass of the substance at its melting point. The heat of fusion is usually expressed in joules per gram (J/g). In this case, a total of 4000 J are needed to melt 8.00 grams of 'X'.
Heat of fusion formula: Heat of Fusion (J/g) = Total Energy Required to Melt (J) / Mass (g)
Thus, the calculation would be 4000 J / 8.00 g, which equals 500 J/g.
The correct answer to the question, "If 4000 J are needed to melt 8.00 grams of X at its melting point, what is the heat of fusion of X?" is b. 500 J/g.