Which of the following substances will be a solid at 20 °C and will melt when placed in a beaker of hot water at 80 °C? | melting point in °C | boiling point in °C | |---------------------|---------------------| | A | 122 | 249 | | B | -7 | 59 | | C | 30 | 2403 | | D | -32 | 27 | (b) A student set up the apparatus shown in Figure 4 to obtain pure water from - Edexcel - GCSE Chemistry - Question 5 - 2018 - Paper 1

To determine which substance will be a solid at 20 °C and will melt at 80 °C, we need to analyze the melting points provided:

1. Substances A, B, C, and D have melting points of 122 °C, -7 °C, 30 °C, and -32 °C respectively.
2. At 20 °C, substances A and C will be in a solid state since their melting points are above 20 °C.
   • Substance A: Melting point is 122 °C (solid at 20 °C).
   • Substance C: Melting point is 30 °C (solid at 20 °C).
3. Additionally, we check if these substances will melt at a temperature of 80 °C:
   • Substance A: Will not melt at 80 °C since it requires a higher temperature.
   • Substance C: Will melt at 80 °C since it is below its melting point of 30 °C.
4. Conclusion: Thus, the correct answer is C (30 °C) as this substance is a solid at 20 °C and will melt when heated in water at 80 °C.