Let's analyze the given chemical reaction to determine which substance is the base:
[tex]\[
H_2SO_4(aq) + Ca(OH)_2(aq) \longrightarrow CaSO_4(aq) + 2H_2O(l)
\][/tex]
### Step-by-Step Solution:
1. Identify the Acids and Bases:
- An acid is a substance that donates protons (H⁺ ions) or accepts electrons.
- A base is a substance that accepts protons (H⁺ ions) or donates hydroxide ions (OH⁻ ions).
2. Determine the Nature of Each Reactant:
- [tex]\(H_2SO_4(aq)\)[/tex] (sulfuric acid) is known to be a strong acid. It dissociates in water to produce H⁺ ions.
- [tex]\(Ca(OH)_2(aq)\)[/tex] (calcium hydroxide) is known to be a base. It dissociates in water to produce OH⁻ ions.
3. Examine the Reaction:
- In the reaction, [tex]\(H_2SO_4(aq)\)[/tex] reacts with [tex]\(Ca(OH)_2(aq)\)[/tex].
- The products of the reaction are [tex]\(CaSO_4(aq)\)[/tex] and [tex]\(2H_2O(l)\)[/tex].
4. Identify the Substance Providing OH⁻ Ions:
- Since a base provides OH⁻ ions in solution, we look for which substance can supply these ions.
- [tex]\(Ca(OH)_2(aq)\)[/tex] dissociates into [tex]\(Ca^{2+}\)[/tex] and [tex]\(2OH⁻\)[/tex]. Therefore, it provides OH⁻ ions in the solution.
From the options given, we can now identify the base in the reaction:
1. [tex]\(2H_2O(l)\)[/tex] – Water, not a base.
2. [tex]\(H_2SO_4(aq)\)[/tex] – Sulfuric acid, an acid.
3. [tex]\(CaSO_4(aq)\)[/tex] – Calcium sulfate, a product, not a base.
4. [tex]\(Ca(OH)_2(aq)\)[/tex] – Calcium hydroxide, which provides OH⁻ ions and is the base.
### Conclusion:
The base in the reaction is [tex]\(Ca(OH)_2(aq)\)[/tex].
Thus, the correct answer is:
[tex]\[ \boxed{Ca(OH)_2(aq)} \][/tex]
