A student decided to silver-plate a locker key using the apparatus shown - VCE - SSCE Chemistry - Question 15 - 2002 - Paper 1

In an electroplating process, silver ions ($Ag^+$) are reduced to silver metal at the cathode, which is where the metal is deposited. In the described setup, the key would act as the cathode in the circuit.

Therefore, the correct choice is:

D. cathode and is connected to the negative terminal of the power supply.