The repetition of property after a certain interval is called?

Periodicity of property means that certain properties of elements repeat themselves after a fixed interval when elements are arranged in order of increasing atomic number. This happens because elements in the same group have similar electron configurations, leading to similar chemical properties.

For example, the atomic size, ionization energy, and electronegativity of elements show regular patterns as you move across a period or down a group in the periodic table.

Other options explained:
- Atomic radius is the size of an atom, not the repetition of property.
- Electron affinity is the energy change when an atom gains an electron.
- None of these is incorrect because the correct term is periodicity of property.

So, the right answer is periodicity of property.