Answer : The formula unit of Sr & Cl is
and the formula unit of Al & S is 
Explanation :
Formula unit : it is defined as the lowest number ratio of ions of an elements in an ionic compound or covalent compound.
For the formula unit of Sr & Cl, two chloride ions
are needed to neutralize the one strontium ion
.
For the formula unit of Al & S, three sulfide ions
are needed to neutralize the two aluminium ion
.
The formula unit of
and
are shown below.
The usual units of density are g/cm.
You may have also seen g/mL used for density. Keep in mind that 1 cm = 1 mL.
Fire transfers heat by CONVECTION, meaning some heat rises, and FALL, meaning some heat goes out in every directions.
Hope that helps!!!