Step 1: Understand oxidation in electrolysis.
In electrolysis, oxidation is the loss of electrons, and it always occurs at the anode. The anode is the electrode where oxidation takes place, and electrons are released into the electrolyte.
Step 2: Compare the options.
- Option (A) Anode: Correct, because oxidation happens at the anode during electrolysis.
- Option (B) Cathode: Incorrect, the cathode is where reduction (gain of electrons) occurs, not oxidation.
- Option (C) Both anode and cathode: Incorrect, oxidation only occurs at the anode.
- Option (D) Depends upon electrolyte used: Incorrect, oxidation always occurs at the anode, regardless of the electrolyte.
Final Answer:
\[
\boxed{\text{Anode}}
\]