List I contains a list of categories of secondary metabolites or proteins, while List II contains examples of specific compounds. Terpenoids are a large class of organic chemicals similar to terpenes, and diterpenes are a type of terpenoids. So, A matches with II. Lectins are a type of protein that can bind specifically to certain sugars and so play a role in recognizing carbohydrates. Concanavalin A is a lectin. So, B matches with IV. Alkaloids are a class of naturally occurring organic compounds that mostly contain basic nitrogen atoms. Codeine is an alkaloid found in opium poppy. So, C matches with I. Toxins are poisonous substances produced within living cells or organisms. Ricin is a toxin. So, D matches with III.