Particles which can be added to the nucleus of an atom without changing its chemical properties are

Correct answer: (a) Neutrons

Explanation

An element's chemical properties depend on its electrons, and the number of electrons in a neutral atom equals the number of protons (the atomic number).

Adding neutrons changes only the mass number, giving an isotope of the same element with the same chemistry. Adding protons would make a different element, and adding electrons would make an ion.