Identify the incorrect pair.

The correct option is Drugs - Ricin.

To identify the incorrect pair, we can analyze the classification of various secondary metabolites:
1. Alkaloids: These are nitrogenous organic compounds of plant origin. Examples include morphine and codeine. Therefore, the pair Alkaloids - Codeine is correct.
2. Toxins: These are poisonous proteins produced by plants and animals. Examples include abrin and ricin. Therefore, the pair Toxin - Abrin is correct.
3. Lectins: These are carbohydrate-binding proteins that agglutinate cells. A well-known plant lectin is concanavalin A. Therefore, the pair Lectins - Concanavalin A is correct.
4. Drugs: Representative secondary metabolites used as drugs include vinblastine (anti-cancer drug) and curcumin. Ricin is a toxin, not a drug. Therefore, the pair Drugs - Ricin is incorrect.