Neutrons:

The neutron is a subatomic hadron ion which has the symbol n or n⁰, no net electric charge and a volume slightly bigger than that of a proton. With the exception of hydrogen-1, nuclei of molecule consist of neutrons and protons, which are therefore collectively known as nucleons. The number of protons in a center of nucleus is the atomic number and describes the kind of element the atom creates. Neutrons are necessary within an atomic nucleus as they related with protons via the intra nuclear force; protons are not able to attach with each other because of their mutual electromagnetic repulsion being harder than the attraction of the nuclear force.