Which one of the following is not a periodic property i.e. does not show any trend on moving from one side to the Other in the periodic table ?

Periodic properties are specific patterns in the periodic table that illustrate trends in element characteristics across periods and groups [t2]. Major periodic trends include atomic size (atomic radius), which generally decreases across a period and increases down a group [t3][t8]. Valency, or the combining capacity of elements, is determined by the number of valence electrons and shows a periodic recurrence based on electronic configuration [c3][t4]. Electronegativity, the tendency of an atom to attract electrons, also follows a clear trend, typically increasing across a period and decreasing down a group [t1][t9]. In contrast, radioactivity is a nuclear property related to the stability of the nucleus and the decay rate of specific nuclides [c5]. It does not show a regular, predictable trend across the periodic table like electronic-shell-dependent properties, making it a non-periodic property.

Sources

1. [1] https://en.wikipedia.org/wiki/Periodic_trends
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 59
3. [3] https://en.wikipedia.org/wiki/Periodic_table
4. [5] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > Period of Radioactivity > p. 83