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 D — Citric or sulfamic acid

Citric or sulfamic acids are preferred for descaling because they are effective at dissolving calcium carbonate and sulfate scales while being significantly less corrosive to the copper-nickel or brass tubes of the evaporator compared to concentrated mineral acids like hydrochloric or sulfuric acid, which can cause severe metal damage.