Identify the incorrect pair.

To determine which pair is incorrect, we examine each pairing and verify whether the listed item correctly belongs to the specified category.

1. Lectins – Concanavalin A
Lectins are carbohydrate‑binding proteins found in many plants. Concanavalin A (often abbreviated as Con A) is a well‑known lectin extracted from the jack‑bean plant. This pairing is correct.

2. Drugs – Ricin
Ricin is a highly toxic protein derived from the seeds of the castor bean plant. It functions as a potent toxin that inhibits protein synthesis, not as a therapeutic drug. Therefore, classifying ricin under “Drugs” is inaccurate, making this pair the incorrect one.

3. Alkaloids – Codeine
Alkaloids are nitrogen‑containing natural compounds that often have pharmacological activity. Codeine is an opiate alkaloid derived from the opium poppy and is used medically as a pain‑relieving drug. This pairing is correct.

4. Toxin – Abrin
Abrin is a toxic protein found in the seeds of the Abrus precatorius plant. It belongs to the same family of ribosome‑inactivating toxins as ricin. Hence, pairing “Toxin” with “Abrin” is accurate.

By evaluating each option, the only mismatched combination is Drugs – Ricin. Ricin is a toxin, not a drug, so this is the incorrect pair.