7．
有\(\rm{5}\)种单核粒子，它们分别是\(\rm{\rlap{{\!\,}^{40}}{{\!\,}_{19}}\boxed{\quad }}\)、\(\rm{\rlap{{\!\,}^{40}}{{\!\,}_{18}}\boxed{\quad }}\)、\(\rm{\rlap{{\!\,}^{40}}{{\!\,}_{19}}\boxed{\quad }^{+}}\)、\(\rm{\rlap{{\!\,}^{40}}{{\!\,}_{20}}\boxed{\quad }^{2+}}\)、\(\rm{\rlap{{\!\,}^{41}}{{\!\,}_{20}}\boxed{\quad }(}\)“\(\rm{\boxed{\quad }}\)”内元素符号未写出\(\rm{)}\)，则它们所属元素种类有( )