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
Atomic number of oxygen: 8 After the IUPAC Tables, 2009 the atomic weight of oxygen is [15,99903; 15,99977]. The abridged conventional atomic weight is (also after the IUPAC â¦Tables, 2009) 15,999; following the IUPAC tradition the correct expression is atomic weight, not atomic mass.