Which one of the following is most likely a mismatch?

Let us check each pair for mismatch:

Zinc - Liquation: Liquation is a method used for purifying metals with low melting points. Zinc is typically purified by electrolysis or distillation, not by liquation. Liquation is used for tin, bismuth, and lead. So this is a mismatch.

Copper - Electrolysis: Copper is commonly refined by electrolytic refining. This is correct.

Nickel - Mond process: The Mond process (using Ni(CO)₄) is used for purifying nickel. This is correct.

Titanium - van Arkel Method: The van Arkel method (iodide decomposition) is used for purifying titanium and zirconium. This is correct.

The mismatch is Option 1: Zinc - Liquation.