It means the relationship between two systems connected only by a diathermic wall.
There are 32 valence electrons for the Lewis structure for ClO4
B the atomic number is 20 and then you subtract atomic mass to find the neutrons
We would use miles to measure the diameter of the earth because that is the greatest measure of length that is possible to measure something large.
If a person weighs 63.4 KG they will weigh 139.773 but if you estimate it which in most cases you do it would be 139.8 :)
