Are atoms defined by the number of protons

The number of protons in an atom is unique to each element. For example, carbon atoms have six protons, hydrogen atoms have one and oxygen atoms have eight. The number of protons in an atom is referred to as the atomic number of that element. The number of protons also determines the chemical behavior of the element.

yes, the number of protons makes an atom whatever element it is, and the number of protons cannot be changed, because changing the number of protons would change what element it is. the number of protons in each element is unique.