Here is the explanation for the correct matching of List I with List II:

I. Blue vitriol - (D) Copper sulphate:

Blue vitriol, also known as copper sulphate, is a chemical compound with the formula CuSO4. It is a blue crystalline solid and is commonly used in various applications such as agriculture, medicine, and as a laboratory reagent.

II. Epsom salt - (C) Magnesium sulphate:

Epsom salt is the common name for magnesium sulphate (MgSO4). It is a white crystalline compound that contains magnesium, sulfur, and oxygen. Epsom salt is widely used in bath salts, as a laxative, and in various agricultural and industrial applications.

III. Baking soda - (A) Sodium bicarbonate:

Baking soda, also known as sodium bicarbonate (NaHCO3), is a white crystalline compound. It is commonly used in baking as a leavening agent, as well as in various household cleaning and personal care products.

IV. Caustic soda - (B) Sodium hydroxide:

Caustic soda, also known as sodium hydroxide (NaOH), is a strong alkaline compound. It is a white solid and is widely used in industries for various purposes, such as in the production of soaps, detergents, paper, and textiles.

By matching the compounds with their corresponding names and uses, we can conclude that:

I. Blue vitriol is synonymous with copper sulphate.

II. Epsom salt is another name for magnesium sulphate.

III. Baking soda refers to sodium bicarbonate.

IV. Caustic soda is synonymous with sodium hydroxide.

Therefore, the correct matching is:

I-D, II-C, III-A, IV-B.