Which of the following acids is preferable and most commonly used for scale removal from the heating surfaces of the jacket-water heated submerged-tube evaporator?

Correct Answer: Option B — Citric or sulfuric acid

Citric or sulfuric acid solutions are preferred for descaling because they effectively dissolve calcium carbonate and magnesium hydroxide scale without causing excessive damage to the copper-nickel or brass tube materials commonly found in submerged-tube evaporators, provided the concentration and temperature are strictly controlled during the cleaning process.