Goblet cells are unicellular glands that secrete mucus, hence statement (I) is correct. Statement (II) is incorrect because exocrine glands secrete substances like enzymes, mucus or sweat through ducts, whereas hormones are secreted by endocrine glands directly into body fluids. Some simple columnar or cuboidal epithelial cells can get modified into glandular epithelium for secretion, making statement (III) incorrect. Compound epithelium consists of several layers of cells and is mainly protective, so its role in secretion and absorption is limited, which makes statement (IV) correct.