Polyanion formation is maximum in Sulphur.

Polyanions are negatively charged ions that contain more than one atom. The formation of polyanions depends on various factors such as the electronegativity of the atom, the number of valence electrons, and the ability to gain electrons to achieve a stable electron configuration.

Sulphur, with the atomic number 16, belongs to Group 16 (Group 6A) of the periodic table. It has six valence electrons in its outermost energy level. To achieve a stable electron configuration, sulphur needs to gain two electrons.

Here are the reasons why polyanion formation is maximum in Sulphur:

1. Electron configuration: Sulphur has six valence electrons in its outer energy level, and it needs to gain two electrons to achieve a stable electron configuration of the nearest noble gas, argon. This makes it easier for sulphur to gain electrons and form negatively charged ions.

2. Electronegativity: Sulphur has a moderate electronegativity, which means it has a tendency to attract electrons towards itself. This property is favorable for the formation of polyanions as it allows sulphur to gain electrons and become negatively charged.

3. Size of the atom: Sulphur is a relatively large atom compared to other elements in Group 16. The larger the atom, the more easily it can accommodate additional electrons and form stable polyanions.

4. Stability of polyanions: Sulphur can form a variety of stable polyanions, such as sulfide ions (S2-), bisulfide ions (HS-), and thiosulfate ions (S2O3^2-). These polyanions have strong bonds and are stable in various chemical reactions.

In contrast, other options like Nitrogen, Oxygen, and Boron do not have the same combination of electron configuration, electronegativity, and size that make polyanion formation as favorable as Sulphur.

In conclusion, Sulphur exhibits maximum polyanion formation due to its electron configuration, moderate electronegativity, ability to accommodate additional electrons, and the stability of the formed polyanions.