Q.Distinguish between rhombic ($\alpha$) sulphur and monoclinic ($\beta$) sulphur.

[!TLDR] Rhombic sulphur (pale yellow, octahedral crystals, stable below 369 K) and monoclinic sulphur (needle-like crystals, stable 369 K to melting) are both built from S8 rings but pack differently, interconverting reversibly at 369 K. [!ANSWER] Rhombic sulphur is stable below 3 …

Both rhombic ($\alpha$-) and monoclinic ($\beta$-) sulphur are built from the identical structural unit -- the puckered, crown-shaped $\text{S}_8$ ring, in which each S-S-S bond angle is close to $105^\circ$ -- but the two forms pack these rings into different crystal lattices. Rhombic sulphur, obtained by slowly evaporating a solution of sulphur in carbon disulphide, crystallises as pale yellow, octahedral-shaped crystals and is the thermodynamically stable form at ordinary room temperature. Monoclinic sulphur, obtained by melting rhombic sulphur and letting it crystallise slowly, forms long, needle-like prismatic crystals from the same $\text{S}_8$ rings packed in a different, less densely ordered arrangement. The two forms interconvert reversibly at a sharp transition temperature of $369\ \text{K}$ ($95.5^\circ\text{C}$): rhombic sulphur is the stable form below this temperature, monoclinic sulphur is …

Note the shared S8-ring building block, then contrast crystal shape, method of formation, and state the transition temp …

Describing rhombic and monoclinic sulphur as different molecules rather than different crystal packings of the same S8 ring; getting the transition t …