Q.vi. Write the names of allotropic forms of selenium.

Sulfur exhibits numerous allotropic forms, of which rhombic sulfur (alpha, stable below 369 K, pale yellow, orthorhombic, m.p. 385.8 K, density about 2.07 g/cm3) and monoclinic sulfur (beta, stable above 369 K, bright yellow, needle-shaped, m.p. 393 K, density about 1.99 g/cm3) are the most important; both are built from the identical puckered, crown-shaped S8 ring (S-S bond length about 204 pm, S-S-S angle about 107 degrees), differing only in how these rings pack in the crystal. Other ring sizes (6 to 20 sulfur atoms) have also been synthesised, including the chair-shaped cyclo-S6; at very high temperature (around 1000 K) the dominant species is instead the diatomic S2 molecule, which -- like O2 -- is paramagnetic, …