There is no cyanosis in severe anemia because -

Ans is 'a' i.e. Certain min. amount of reduced Hb should be present o Cyanosis is a blue coloration of the skin and mucous membranes due to the presence of >5g/dl reduced hemoglobin in blood vessels near the skin surface. Now since in anemia the total amount of hemoglobin is decreased, the amount of reduced Hb to produce Cyanosis is not sufficient.