Vitamin K antagonists (VKA) are a group of substances that reduce blood clotting by reducing the action of vitamin K. They are used as anticoagulant medications in the prevention of thrombosis, and in pest control, as rodenticides. 1  1 Mechanism of action.  2 Coumarins (4-hydroxycoumarins)
Calculate the average atomic mass of oxygen. Solution: ((15.994915*99.757) + (16.999132*0.038) + (17.999160*0.205))/100 = 15.999405 . Using our equation for determining average atomic mass, we see that the average atomic mass for oxygen is 15.999405 amu. If we check the periodic table, we will see that our average atomic mass is the same as the atomic mass indicated on the element oxygen. Ã
The unit that is used for the average atomic mass is amu (atomic mass unit). Oxygen has three isotopes: oxygen-16, which has an atomic mass of 15.994915 amu and a natural abundance of 99.757%, oxygen-17, which has an atomic mass of 16.999132 amu and a natural abundance of 0.038%, and oxygen-18, which has an atomic mass of 17.999160 amu and a natural abundance of 0.205%.