Blister copper is:
[A] Electrically refined copper
[B] A mixture of copper and silver
[C] Copper containing 2% impurity
[D] Present in the anode mud in an electrolytic process

Hint: For extraction of copper from the sulphide ores, the process of smelting is used. Blister copper is the purest form of copper after electrically refined copper (100% pure) which is obtained in this process.

Complete step by step solution:
> In the process of copper extraction, Copper matte which is a combination of copper sulphide and iron sulphide is extracted prior to the final step, which on reduction forms blister copper. The copper matte usually contains 30%-70% copper mostly as copper sulphide but also as iron sulphide.
> At very high temperature, the sulphur is removed as sulphur dioxide by blowing air through the molten matte.
     \[2C{{u}_{2}}S+3{{O}_{2}}\to 2C{{u}_{2}}O+2S{{O}_{2}}\]
     \[2C{{u}_{2}}O+C{{u}_{2}}S\to 6Cu+S{{O}_{2}}\]
The copper thus formed is known as blister copper.
> It is called “Blister Copper” due to the broken surface formed when the sulphur dioxide present in it tries to escape as it solidifies.
> Blister copper is around 98-99.55% pure .It contains impurities mainly of iron but other impurities such as Arsenic, Zinc, Lead, Gold and silver might also be present.
Therefore, Option [C] Copper containing 2% impurity is the correct answer.

ADDITIONAL INFORMATION:
The blister copper formed in the Bessemerization process is further purified by electrolysis. The blister copper is kept as anode and sheets of pure copper are the cathodes which are covered with graphite. A mixture of Copper sulphate with a little amount of Sulphuric acid is used as the electrolyte. During electrolysis, the soluble impurities fall to the bottom of the cell and pure copper is deposited on the cathode plates.

NOTE: Here, it is important to remember that blister copper is not the electrically refined copper. Electrically refined copper is 100% pure but blister copper is not, although it contains very little amount of impurities.