Which process causes oil droplets to merge into larger droplets during treatment?

• A. Hydration
• B. Coalescence
• C. Ostwald Ripening
• D. Evaporation

Answer: (B)

Coalescence is the process where droplets collide and fuse to form larger droplets. In oil–water treatment, turbulence, mixing, and flow cause small oil droplets to come into contact. When they touch, the thin oil film between them breaks or drains away, allowing the droplets to merge into a bigger drop. This growth in droplet size helps the oil separate more easily by gravity or flotation because larger droplets rise or settle faster and have less surface area to volume ratio.

Hydration doesn’t drive droplet fusion; Ostwald ripening is a slower mass-transfer process where smaller droplets dissolve and redeposit onto larger ones through the water, rather than by direct collision and fusion. Evaporation would remove volatile components, not merge droplets. So the merging into larger droplets during treatment is explained by coalescence.