Ans. (a) Coagulative necrosisRef. Robbiti's pathology 9th ed. /41-43, 50COAGULATIVE NECROSIS* This pattern of necrosis is typically seen in hypoxic environments, such as infarction.* Coagulative necrosis occurs primarily in tissues such as the kidney, heart and adrenal glands.* Severe ischemia most commonly causes coagulative necrosis.* Coagulation occurs as a result of protein denaturation, causing the albumin in protein to form a firm and opaque state.* It is characterized by the formation of a gelatinous (gel- like) substance in dead tissues in which the architecture of the tissue is maintained, and can be observed by light microscopy.Also KnowQUEFACTIVE NECROSIS* It is characterized by the digestion of dead cells to form a viscous liquid mass. This is typical of bacterial, or sometimes fungal, infections because of their ability to stimulate an inflammatory response.* The necrotic liquid mass is frequently creamy yellow due to the presence of dead leukocytes and is commonly known as pus.* Hypoxic infarcts in the brain presents as this type of necrosis, because the brain contains little connective tissue but high amounts of digestive enzymes and lipids, and cells therefore can be readily digested by their own enzymes.CASEOUS NECROSIS* It can be considered a combination of coagulative and liquefactive necroses, typically caused by mycobacteria, fungi and some foreign substances.* The necrotic tissue appears as white and friable, like clumped cheese.* Microscopic examination shows amorphous granular debris enclosed within a distinctive inflammatory border. Granuloma has this characteristic.FAT NECROSIS* It is specialized necrosis of fat tissue, resulting from the action of activated lipases on fatty tissues such as the pancreas.* In the pancreas it leads to acute pancreatitis, a condition where the pancreatic enzymes leak out into the peritoneal cavity, and liquefy the membrane by splitting the triglyceride esters into fatty acids through fat saponification.* Calcium, magnesium or sodium may bind to these lesions to produce a chalky-white substance. The calcium deposits are microscopically distinctive and may be large enough to be visible on radiographic examinations. To the naked eye, calcium deposits appear as gritty white flecks.Fibrinoid necrosis is a special form of necrosis usually caused by immune-mediated vascular damage. It is marked by complexes of antigen and antibodies, sometimes referred to as "immune complexes" deposited within arterial walls together with fibrin.