Blister copper is

CONCEPT:

Blister Copper

• Blister copper is a term used in metallurgy to describe a form of copper that is produced as an intermediate stage in the refining process of copper.
• It is called 'blister copper' because of its characteristic blisters on the surface, which are caused by the release of sulfur dioxide gas during the smelting process.

EXPLANATION:

• Blister copper is not pure copper; it contains impurities.
• It is also not a copper alloy, as it primarily consists of copper with a small percentage of impurities.
• The composition of blister copper is typically around 98-99% copper, with the remaining 1-2% being impurities such as sulfur, iron, and other metals.
• The impurities in blister copper give it a characteristic blistered appearance, which is why it is named so.

Therefore, the correct answer is option 4: Cu having 1% impurity.