When fireworks explode, what is happening to the
fireworks?

Will they cause a physical change, chemical change, or a thermal change?

because of all the things that happen around the us, many people get into arguments which sadly could get physical, but we should actually make a change for that.

a corroding iron, if that's one of your choices

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.