The functions of antihistamine are:

Antihistamines are drugs that diminish or abolish the main actions of histamine released in the body. Histamine is released during allergic reactions and also stimulates gastric acid secretion.

Antihistamines serve two primary functions. First, they act as antiallergic agents by blocking $$H_1$$ receptors, which helps relieve symptoms such as runny nose, sneezing, itching, and swelling caused by allergic reactions. Second, certain antihistamines (specifically $$H_2$$ receptor blockers like cimetidine and ranitidine) act as antacids by reducing the secretion of hydrochloric acid in the stomach, thereby treating conditions like peptic ulcers.

Option (1) is incorrect because analgesic (pain relief) is not a function of antihistamines. Option (3) is incorrect for the same reason. Option (4) is incorrect because antidepressant activity is not a primary function of antihistamines.

Hence, the correct answer is option (2): Antacid and Antiallergic.