Correct Option
The correct option is To remove gangue based on property differences.
Explanation
Ores mined from the earth are naturally contaminated with large quantities of impurities such as soil, sand, and rocky materials. These impurities are collectively referred to as gangue. The process of removing these impurities to increase the percentage of metal in the ore is known as the enrichment or concentration of ore.
Option Analysis
- To remove gangue based on property differences is Correct: The primary objective of enrichment is the removal of gangue. The specific techniques used (such as hydraulic washing, magnetic separation, froth flotation, or leaching) are chosen based on the differences in physical or chemical properties between the metal compound and the gangue.
- To increase oxidation state of metal is Incorrect: Increasing the oxidation state or converting the metal compound usually occurs in subsequent steps like roasting or calcination, not during the initial physical concentration.
- To convert ore to alloys is Incorrect: Alloys are homogeneous mixtures created after the metal has been fully extracted and refined. This is a post-extraction application.
- To dissolve the ore completely is Incorrect: While specific methods like leaching involve dissolving the ore chemically to separate it from insoluble impurities, dissolving is a method, not the universal purpose. The fundamental purpose remains the removal of impurities.
Key Takeaway
Enrichment of ore is the preliminary step in metallurgy aimed strictly at removing gangue (impurities) based on differences in physical or chemical properties, thereby concentrating the metal content.