The Brainliest Answer!
Short Answer : Electrons

Long Answer : However, the properties of the electrons of an atom are determined in large part by the number of protons present in the nucleus of the atom. The number of neutrons generally has a neglegible effect upon the properties of the electrons which are of chemical significance.
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Its atomic  mass, number, valency and how many e-, p+ and neutrons and present
But protons and neutrons do not directly tell about the chemical properties 
if you will see chemical reactions then it will be donated or recived
so basically they participate in reactions and determine how a chemical will react.