**Core Concept**
Gastric lavage is a procedure used to remove substances from the stomach after ingestion. However, its application is limited due to potential complications and specific contraindications. The underlying principle being tested here is the identification of situations where gastric lavage is not recommended.

**Why the Correct Answer is Right**
Gastric lavage is contraindicated in cases of poisoning by corrosive substances, particularly strong acids and bases. The ingestion of such substances can cause severe mucosal damage and perforation of the esophagus or stomach. Performing gastric lavage in this scenario can exacerbate the damage and lead to further complications. The esophageal or gastric mucosa is highly susceptible to injury from these corrosives.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because gastric lavage is not contraindicated in poisoning by opioids. In fact, gastric lavage may be considered in cases of opioid overdose if performed promptly and within a certain time frame.
* **Option B:** This option is incorrect because gastric lavage is not contraindicated in poisoning by sedatives. However, caution is advised due to the potential for aspiration of gastric contents.
* **Option C:** This option is incorrect because gastric lavage is not contraindicated in poisoning by salicylates. In fact, gastric lavage may be considered in cases of salicylate overdose if performed promptly and within a certain time frame.

**Clinical Pearl / High-Yield Fact**
When considering gastric lavage, it's essential to remember the "3 Ts": time (the sooner the better), type (gastric lavage is more effective for substances that are poorly absorbed or have a narrow therapeutic index), and toxic amount (gastric lavage is less effective for large ingestions).

**Correct Answer: C. Corrosive substances. Corrosive substances.**