Final answer:
The solubility of HCl and NH4Cl in 100 grams of water at a specific temperature cannot be determined based on the given information.
Step-by-step explanation:
The solubility of a compound depends on several factors, including temperature. In general, as temperature increases, the solubility of most compounds also increases. However, there are exceptions to this trend. In the case of hydrogen chloride (HCl) and ammonium chloride (NH4Cl), their solubilities in water at different temperatures can be compared using a solubility curve.
Based on the provided information and graph of solubility against temperature, it is not possible to determine the exact temperature at which HCl and NH4Cl will have the same solubility in 100 grams of water. Therefore, none of the given options (a) 50°C, (b) 75°C, (c) 100°C, or (d) 25°C can be determined as the correct answer.