Caustic poison erodes mucosa because

B i.e. Hygroscopic in nature Caustic alkalis are the commonest cause of chemical burns. The hydroxyl ion produces a saponification of fat, soluble alkaline proteinases, cellular dehydration hygroscopic excrating water from tissues)Q, exothermic reaction, coagulation of cellular proteins and conversion of hemoglobin into haematin. Mainly in the local tissues of alimentary tract (or rarely respiratory) mucosa.