B.
This method of expressing concentration is employed with solutions where both the solute and solvent are liquid. This is because it is easy to measure the volume of a liquid compared to that of a solid. Usually weight/weight is used in concentrations involving only solids.
So in one hour half the amount remains (that's what half life means). In two hours 1/4 (or half of half) would remain and in three hours 1/8 would remain.
So the answer is 1/8
B) they have no charges and are inside an atom.*
FeCl₂ + 2NH₄OH → Fe(OH)₂ + 2NH₄Cl
True, if you would like an example look at Indian arrow heads or early architecture all use rocks.
