Q.i. Distinguish between rhombic sulfur and monoclinic sulfur.

Colour and shape. Rhombic (alpha) sulfur is pale yellow and forms orthorhombic crystals; monoclinic (beta) sulfur is bright yellow and forms needle-shaped monoclinic crystals.

Melting point and density. Rhombic sulfur melts at 385.8 K and has a density of about 2.07 g/cm3; monoclinic sulfur melts at the slightly higher 393 K but has a lower density, about 1.99 g/cm3.

Solubility. Rhombic sulfur is insoluble in water but soluble in CS2; monoclinic sulfur is likewise soluble in CS2.

Stability. Rhombic sulfur is the thermodynamically stable form below 369 K, transforming into monoclinic sulfur above this temperature; monoclinic sulfur is stable above 369 K and reverts to rhombic sulfur on cooling below it.

Structure. Both allotropes are built from the identical S8 puckered (crown-shaped) ring molecule -- their differences arise purely from how these S8 rings pack together in the crystal lattice, not from any difference in the molecular unit itself.

Preparation. Rhombic sulfur is obtained by evaporating a solution of roll sulfur in CS2; monoclinic sulfur is obtained by melting rhombic sulfur, letting a crust form on cooling, then draining the still-liquid sulfur from beneath the crust to leave needle-shaped crystals.

Working systematically through Table 7.7's six comparison points (colour, shape, m.p., density, solubility, stability/structure) for the two sulfur allotropes.

• Assuming the two allotropes have different underlying molecules; both are genuinely S8 rings, differing only in solid-state packing, not in molecular formula.