Which one of the following polymers is not obtained by condensation polymerisation?

An element crystallises in a face-centred cubic (fcc) unit cell with cell edge $$a$$. The distance between the centres of two nearest octahedral voids in the crystal lattice is :

Consider the complex ions,
trans-[Co(en)₂Cl₂]⁺ (A) and
cis-[Co(en)₂Cl₂]⁺ (B).
The correct statement regarding them is :

The correct order of the ionic radii of
O^2–, N^3–, F^– , Mg²⁺, Na⁺ and Al³⁺ is :