What are isotones and isomers ?

Isotones : The nuclei having the same neutron number (N), but different atomic numbers (Z) are called isotones.
Ex : ${ }_{20}^{40}\mathrm{Ca}{,}_{19}^{39}\mathrm{K}$ are the isotones with same neutron number. N = A – Z = 20
Isomers : The nuclei having same atomic number (Z) and same mass number (A), but different nuclear properties.
Ex : ${ }_{35}^{80}{\mathrm{Br}}^{\mathrm{m}}{,}_{35}^{80}{\mathrm{Br}}^{\mathrm{g}}$ are isomers.