Recall the electrolytic refining of copper

In electrolytic refining of copper:

• Impure copper is made the anode
• Pure copper sheet is made the cathode
• The electrolyte is acidified aqueous $\mathrm{CuSO_4}$

The electrode reactions are:

At anode: $\mathrm{Cu(s) \rightarrow Cu^{2+}(aq) + 2e^-}$

At cathode: $\mathrm{Cu^{2+}(aq) + 2e^- \rightarrow Cu(s)}$

Evaluate each option

A: Impure Cu strip is used as cathode

• This is incorrect.
• In copper refining, impure copper is the anode, not the cathode.

Therefore, A is false.

B: Acidified aqueous $\mathrm{CuSO_4}$ is used as electrolyte

• This is the standard electrolyte used in electrolytic refining of copper.

Therefore, B is true.

C: Pure Cu deposits at cathode

• Copper ions from solution gain electrons at the cathode and deposit as pure copper: $\mathrm{Cu^{2+} + 2e^- \rightarrow Cu}$

Therefore, C is true.

D: Impurities settle as anode–mud

• Insoluble impurities such as Ag, Au, Pt, etc. fall below the anode as anode mud.

Therefore, D is true.

Final derived answer

The correct statements are: $\boxed{\text{B, C, D}}$

Comparison with stored correct answer

Stored correct answer: B, C, D

My derived answer matches the stored answer.