Step 1: Understanding the Question:
Tannins are divided into two main classes, hydrolysable and condensed, and this question checks four statements, A, B, C and D, about their reactions and solubility.
Step 2: Key Formula or Approach:
Classify each statement by which class of tannin it describes and then check it against the known breakdown products and physical properties of that class.
Step 3: Detailed Explanation:
Statement A concerns a general property shared by both tannin classes: their phenolic hydroxyl groups bind strongly to the nitrogen of alkaloids and to proteins, causing precipitation, so A is true.
Statement B concerns hydrolysable tannins specifically, which are esters of gallic acid or its derivatives with sugars, and hydrolysis, whether acid or enzymatic, breaks these esters down to release gallic acid and ellagic acid, so B is true.
Statement C concerns condensed tannins, which are polymers of flavan units, and strong acid or enzymatic treatment converts them into red brown insoluble phlobaphenes rather than simple acids, so C is true.
Statement D claims tannins are insoluble in water, but tannins are actually quite soluble in water and in alcohol, which is why aqueous decoctions are used for tests like the gelatin test and ferric chloride test, so D is false.
This leaves A, B and C as the correct statements.
Step 4: Final Answer:
A, B and C are correct.