**Question:** False about Hydrocyanic acid.

A. Hydrocyanic acid is a naturally occurring chemical compound.
B. Hydrocyanic acid is a strong acid that dissociates completely in water.
C. Hydrocyanic acid is a poisonous substance and can be found in prussic acid form in cyanide-producing plants.
D. Hydrocyanic acid is used as a food preservative.

**Correct Answer:** D. Hydrocyanic acid is used as a food preservative.

**Core Concept:** Hydrocyanic acid is a toxic, colorless, and highly volatile liquid chemical compound that belongs to the cyanide group. While it does occur naturally in some cyanide-producing plants, it is not a common or easily accessible source for human consumption.

**Why the Correct Answer is Right:** Hydrocyanic acid is used as a food preservative because of its ability to inhibit bacterial growth and extend the shelf life of food products. However, this application raises concerns about safety and toxicity. The correct answer is D, as it highlights the practical use of hydrocyanic acid in food preservation.

**Why Each Wrong Option is Incorrect:**

A. Hydrocyanic acid is not naturally occurring in food, as it is a toxic compound primarily found in certain plants.
B. Hydrocyanic acid is indeed a strong acid and dissociates completely in water, but using it as a food preservative is not safe due to its toxicity.
C. While hydrocyanic acid can be found in cyanide-producing plants, this option is irrelevant to its use as a food preservative.

**Clinical Pearl / High-Yield Fact:** Hydrocyanic acid is highly toxic and lethal in small doses. It is toxic to humans and other mammals and can cause cyanide poisoning, leading to severe neurological, cardiovascular, and respiratory effects. Therefore, using hydrocyanic acid as a food preservative is not recommended due to its severe toxicity and potential health risks to consumers.