Step 1: What is HLB value? HLB stands for Hydrophile-Lipophile Balance. It is a numerical scale (0–20) that tells us how hydrophilic or lipophilic a surfactant is. Higher HLB = more water-loving. Lower HLB = more oil-loving.
Step 3: Why O/W emulsions need HLB 8–18. In an Oil-in-Water emulsion, oil droplets are dispersed in water. A hydrophilic (high-HLB) surfactant preferentially sits at the oil-water interface with its head pointing toward water, stabilising the oil droplets inside the aqueous continuous phase.
Step 4: Eliminate wrong options. HLB 1–3 favours antifoaming. HLB 7–9 is for wetting agents (overlap, but not the standard O/W range). HLB 3–6 is for W/O emulsions. So 8–18 is the correct answer for O/W emulsions.
Step 5: Conclusion. Always remember: high HLB (8–18) for O/W; low HLB (3–6) for W/O.