14) C

A important aspect you have to take into consideration before answering this question is the terms being used in the electrolytes: ‘aqueous’ and ‘molten’

Aqueous means that it is in solution water, meaning it will react with water.

Molten means the pure compound is being electrolysed.

A – The compound is aqueous. Calcium is more reactive than hydrogen, meaning hydrogen would be the product at the cathode 

B – Oxygen would be the product at the anode

C – This is correct. Potassium is more reactive than hydrogen, meaning hydrogen would form at the cathode whilst oxygen would be formed at the anode

D – Aluminium would be the product at the cathode whilst oxygen would be the product at then anode. The two are at the wrong positions

E – there is no hydrogen in molten sodium chloride. So hydrogen should not be the product at the cathode.