Given the mass of aluminum sulfide
= 21.0 g
Molar mass of
= 
Calculating the moles of
:

Each mole
has 3 mol S.
Each mole S constitutes 
Calculating atoms of S in 0.14 mol
:

= 
A. 3
From 0 to 6, a solution is acidic. 7 is neutral and from 8 to 14.. is basic
Characteristics of a Precipitate:
A precipitate is characterized by the following properties:
Appears as a solid species.
Settled down at the bottom of the reaction pot.
Insoluble in the corresponding solvent.
I would say D, because you need to start with nothing to measure the different sizes as they start to grow. hope this helps!