Ans. is 'a' i.e., Seen on dependent parts of body * Postmortem staining refers to discoloration of skin and internal organs after death due to accumulation of fluid blood in toneless capillaries and small veins of dependent part of the body.* As dead body behaves like an inert substance, therefore there is gravitational flow of blood to the dependent parts of body, causing stagnation of blood in toneless capillaries and small veins, causing bluish purple staining of these parts.* Characteristic features of postmortem staining are:1) It does not appear elevated above the surface but has sharply defined (usually horizontal) margins.2) It is an early sign of death. It starts at about 1 hour, becomes a series of mottled patches within 1-3 hours and these pathces increase in size to coalesce in about 3-6 hours. After 6-12 hours, lividity is fully developed and fixed (unchangeable), i.e. primary lividity. It ends when putrification sets in. Fixation of lividity is due to stagnation of blood in distended capillaries and venules (not due to coagulation of blood).3) If the position of body is changed, after development of lividity but before it becomes fixed, these patches will disappear and fresh ones will develop in the new dependent areas (secondary lividity), but lividity to a slight degree will remain in the original area due to staining of tissue by hemolysis (complete).4) Normally the staining is at first bluish-pink and afterwards bluish purple.In severe anemia, and death from haemorrhage, the staining is very faint. In deaths from asphyxia, where blood is deoxygenated and may not readily coagulate, the staining is intensely developed and purple in colour. In conditions where blood coagulates quickly eg. in lobar pneumonia lividity is less abvious.5) It is seen on dependent parts of the body, therefore site depends upon position of body after death:i) In supine: On posterior dependent portion of body. But not seen on back of shoulder blades, buttocks and back of calves due to contact flattening, i.e. toneless capillaries are compressed and occluded by weight and pressure of body.ii) In hanging: Dependent lower half of both lower limb and upper limb (i.e. lower half of leg with feet and lower half of forearm with hands), and external genitalia.iii) In drowning: Head and upper half of body as head being the heaviest part becomes the dependent part. It does not develop in running water due to constantly changing position of the body.6) No lividity is seen on pressure points of body, i.e. contact pallor, as pressure caused by weight of body causes compression of toneless vessels and prevent their filling with blood:i) In supine: No lividity is seen on back of shoulder blades, buttocks, occipital area and calf ->> contact flattening.ii) Also no lividity occurs in parts tightly tied with belt, waist band or brassiere and the area is seen as stripes or bands called vibices.