What are the basis of making symbols

1/ Using the first letter of the name of the elements.

2/  If the name of two or more elements begins with the same letter,the second letter of their name is also taken with first letter.

3/ Symbols are made by using the letters of the name of elements in other languages also.

answerleaving cheese out to get moldy;

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.