Which is a property that most nonmetals have in common

Some physical properties that metals have in common are that they have luster, good thermal and electrical conductivity, high densities and melting points and are malleable. With the exception of mercury, most metals also are solid at room temperature.

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.