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
:

= 
Compounds are substances made of at least 2 different elements. Molecules have at least 2 atoms, doesn't have to be different elements. Compounds and molecules both work.
Answer:
part 1 is from the article
Explanation:
The solution before dilution and after dilution contains same number of moles, and water is added for dilution.
Option B
<h3><u>Explanation:</u></h3>
Suppose before dilution, the solution contains x moles of KCl in Y liter of water. Now as the concentration got halved, then the solution contains x moles of KCl in 2Y kiters of solution. So the number of moles of KCl in the solution remained constant.
Again, as the solution is diluted to half of the concentration, water must have been added with the solution to make it dilute.
CH2OHCH2OH is a
general example of a polyhydroxyl alcohol. A polyhydroxyl alchol is one in which
there are two hydroxyl groups present in the substance. The –OH group attached
to both the carbon atoms.