Step 1: Recall the oil painting medium:
Oil colours are made by grinding pigments in a drying oil. The oil used is linseed oil, pressed from flax seeds.
Step 2: Why linseed oil:
Linseed oil dries slowly and forms a hard, glossy, lasting film. Artists also use it to thin the paint.
Step 3: Check the other options:
(A) Mustard oil and (B) Coconut oil are cooking oils. They stay sticky and never dry into a firm paint film.
(C) Olive oil is also a kitchen oil. It dries very poorly, so the paint would stay soft and crack or smear.
Final Answer:
(D) Linseed oil