(N/A) The stable form of sulfur at room temperature is rhombic sulfur,which transforms into monoclinic sulfur when heated to $369 \ K$.
Rhombic sulfur ($\alpha$-sulfur):
This allotrope is yellow in color,with a melting point of $385.8 \ K$ and a specific gravity of $2.06$.
It is prepared by evaporating the solution of roll sulfur in $CS_2$.
It is insoluble in water but slightly soluble in benzene,alcohol,and ether.
It is readily soluble in $CS_2$.
Monoclinic sulfur ($\beta$-sulfur):
Its melting point is $393 \ K$ and its specific gravity is $1.98$.
It is soluble in $CS_2$.
This form is prepared by melting rhombic sulfur in a dish and cooling it until a crust is formed. Two holes are made in the crust,and the remaining liquid is poured out.
Upon removing the crust,colorless needle-shaped crystals of $\beta$-sulfur are formed. It is stable above $369 \ K$ and transforms into $\alpha$-sulfur below this temperature.
Conversely,$\alpha$-sulfur is stable below $369 \ K$ and transforms into $\beta$-sulfur above this temperature.