What distinguishes a substance from a mixture? a) samples of the same substance can have different intensive properties. b) mixtures are groupings of elements, and compounds are not. c)substances are compounds, and mixtures are not. d) mixtures can be separated physically, while compounds cannot.

The main difference between a mixture and compound is that Mixtures can be separated physically, while compounds cannot.

Mixtures are physically combined things that can be broken down back into their original components. (Think of Salad)

While substances have a chemical composition that can not be physically separated

answer is: nuclear fusion produces elements that are heavier than helium.

nuclei combine to form a heavier nucleus, releasing energy.  

for example, fusion of hydrogen atoms at the sun.  

this fusion nuclear reaction is in the inner core of the sun and hydrogen (atomic number 1) is conveted into helium (atomic number 2).  

the inner core is the central region of the sun and all solar energy is produced in the core by nuclear fusion.