What kind of mixture is sometimes difficult to distinguish form a compound? Why?

Acm ruler with main graduations from 1 to 10 from left to right there are 10 secondary graduations between each of the main graduations there is a line that begins. at the left end of the ruler 10 secondary graduations to the left of the “1 main graduation the right end of the line ends on the eighth secondary graduation to the right of 3 how long is the line

What the blanks in these lines are ?

What does the field of thermodynamics relate to a-changes in nuclear reactions b- changes in energy in systems c changes in molecular structure d changes in atomic properties