What subatomic particle determines the identity of an element

Proton

Explanation:

Proton is a subatomic particle and determines the identity of an element. each element is identified by its atomic number. In an element, the number of protons in the nuclei of the atoms of the element is same as the atomic number of that element and this number is different for each element. for example, Boron has 5 protons in its nuclei, hence the atomic number of the element is 5.