The atomic mass of element is the weighted average atomic mass of the element with respect to the abundance of the isotopes of that element
atomic mass is the sum of the products of the mass of isotopes by their percentage abundance
atomic mass = 15.000 amu x 5.000 % + 16.000 amu x 95.000 %
= 0.7500 + 15.200
atomic mass of element is therefore 15.950
The density of water is a physical property.
You can measure it without changing the water to a different substance.
It is <em>not a physical change</em> because the water does not change to ice or steam.
You can observe a <em>chemical property</em> or a <em>chemical change</em> only if the water <em>changes to a different substance</em>.
