Let's identify which of the given compounds is an alkali.
An alkali is a substance that dissolves in water to form a solution with a pH greater than 7. Typically, alkalis are bases that are soluble in water. Common examples include sodium hydroxide (NaOH) and potassium hydroxide (KOH).
Now, let's analyze each option:
a. CaO (Calcium oxide): This is also known as quicklime. Although it reacts with water to form calcium hydroxide (which is an alkali), in its given dry form as CaO, it is not classified as an alkali.
b. [tex]$CaCP_3$[/tex]: This seems to be a typographical error and is likely meant to be [tex]$CaCO_3$[/tex], which is calcium carbonate. Calcium carbonate is a common substance found in rocks as the minerals calcite and aragonite. It does not dissolve well in water and is not classified as an alkali.
c. [tex]$Ca(OH)_2$[/tex] (Calcium hydroxide): Also known as slaked lime, this compound is a strong base and dissolves in water to form an alkaline solution (a solution with a high pH). Therefore, [tex]$Ca(OH)_2$[/tex] is an alkali.
d. [tex]$CaSO_4$[/tex] (Calcium sulfate): This is a salt commonly found in minerals such as gypsum. It is not soluble in water to a significant degree and is not classified as an alkali.
Hence, the correct answer is:
c. [tex]$Ca(OH)_2$[/tex]
