Which pure substance can be classified as an element? H2
NO3
NaCl
H2SO4

who is bored and wants 2 talk

i'm not sure

explanation:

i'll try whatever you got

answerlinnaeus;

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.