Correct option is (1) Primary
Denaturation of proteins: When protein in native form is subjected to a physical change like temperature or pH, the H-bonds are disturbed. As a result globules get unfold and helices get uncoiled therefore proteins loses its activity. During denaturation 2° and 3° structures get destroyed but 1° structure remain the same.
Ex: Coagulation of egg while on boiling and curdling of milk caused by bacteria present in milk.
