The refining method used when the metal and the impurities have low and high melting temperatures, respectively, is :

Solution

Chemistry ma’am · 3 steps

The metal melts first and runs off, while the impurities stay behind as solid: that is liquation.

1. Use the melting gap. Here the metal melts at a low temperature and the impurities melt at a high one. Heat the impure metal just above the metal's melting point and only the metal turns liquid.
2. How liquation works. The impure metal is placed on the sloping hearth of a furnace and heated. The molten metal flows down the slope and is collected, while the infusible impurities are left on the hearth. Tin, lead and bismuth are refined this way.

   Method	Property it uses
   Liquation	Metal has a low melting point, impurities have a high one
   Distillation	Metal has a low boiling point and is volatile (Zn, Hg)
   Zone refining	Impurities are more soluble in the melt than in the solid metal
   Vapour phase refining	Metal forms a volatile compound that decomposes easily (Ni, Zr, Ti)

3. So. A low-melting metal with high-melting impurities is refined by liquation, option (a).

The idea to keep. Match each refining method to the one property it uses: melting point for liquation, boiling point for distillation, solubility in the melt for zone refining, a volatile compound for vapour phase refining.

Answer from the NTA final answer key. Solution by PrepWiser.