Approach by asking whether each method helps droplets coalesce or keeps them apart:
A crude oil water emulsion only breaks apart when the small dispersed water droplets are given a way to find each other, touch, and merge into bigger drops that settle out. So each proposed method can be judged by a simple question, does it help droplets merge together, or does it keep them apart as fine droplets.
Judging heating by this test:
Heat thins the oil phase so droplets move around and bump into each other more easily, and it softens the stabilizing skin around each droplet so that once droplets touch, they actually merge instead of just bouncing off. Heating clearly helps coalescence, so it passes the test for a separation method.
Judging centrifugation by this test:
A centrifuge does not change the droplets chemically, but it applies a strong artificial force field that rapidly drives the heavier water droplets toward the outer wall of the spinning vessel, away from the lighter oil. This forced, rapid segregation of the two phases is a direct physical route to separation, so centrifugation passes the test.
Judging interfacial tension reducing agents by this test:
Interfacial tension is the very quantity that resists breaking a liquid into fine droplets within another liquid, a high interfacial tension favors large drops and quick separation, while a low interfacial tension favors many small, stable droplets that resist merging. Deliberately lowering this tension therefore works against coalescence and keeps the emulsion finely dispersed, so this option fails the test and does not aid separation.
Judging electrostatic coalescence by this test:
An applied electric field stretches and polarizes each water droplet, and neighboring droplets with induced opposite charges are pulled strongly toward one another until they touch and merge into a single larger droplet. This is a direct, deliberate mechanism for forcing coalescence, so it clearly passes the test.
Final Answer:
\[ \boxed{\text{Heating, Centrifugation, and Electrostatic coalescence}} \]