Answer: The average atomic mass of oxygen is 15.999 amu
Explanation:
Mass of isotope O-16 = 15.995 amu
% abundance of isotope O-16= 99.759 % = 
Mass of isotope O-17 = 16.995 amu
% abundance of isotope O-17 = 0.037% = 
Mass of isotope O-18 = 17.999 amu
% abundance of isotope O-18 = 0.204% = 
Formula used for average atomic mass of an element :

![A=\sum[(15.995\times 0.99759)+(16.995\times 0.00037)+(17.999 \times 0.00204)]](https://tex.z-dn.net/?f=A%3D%5Csum%5B%2815.995%5Ctimes%200.99759%29%2B%2816.995%5Ctimes%200.00037%29%2B%2817.999%20%5Ctimes%200.00204%29%5D)

Thus the average atomic mass of oxygen is 15.999 amu
Answer:
Energy cannot be created or destroyed.
Explanation:
According to the law of conservation of energy, energy can neither be created nor it can be destroyed. Energy can only be transformed from one matter to another. The conservation of energy remains constant in an isolated system. The law is applicable in the system that does not exchange energy in the environment. Energy changes its form but remains constant.