Identify the incorrect pair.

The correct answer is Drugs - Ricin.

To identify the incorrect pair, we can analyze the classification of various biomolecules and secondary metabolites found in plants:

1. Alkaloids - Codeine: Alkaloids are a group of naturally occurring chemical compounds that mostly contain basic nitrogen atoms. Codeine and morphine are well-known examples of alkaloids derived from the opium poppy. Thus, this is a correct pair.
2. Toxin - Abrin: Toxins are poisonous substances produced by living cells or organisms. Abrin is an extremely toxic plant protein found in the seeds of the rosary pea (Abrus precatorius). Thus, this is a correct pair.
3. Lectins - Concanavalin A: Lectins are carbohydrate-binding proteins that are highly specific for sugar groups. Concanavalin A is a well-studied lectin extracted from the jack bean. Thus, this is a correct pair.
4. Drugs - Ricin: Ricin is a highly potent toxin extracted from the seeds of the castor oil plant (Ricinus communis). It is classified under toxins, not drugs. Common examples of plant-derived metabolites used as drugs include vinblastine and curcumin. Therefore, this pair is incorrect.