Let's analyze the given chemical reaction step by step to determine which characteristic of a base it demonstrates:
[tex]\[ CuSO_4(aq) + 2 NaOH(aq) \rightarrow Cu(OH)_2(s) + Na_2SO_4(aq) \][/tex]
1. Reactants Identification:
- [tex]\( CuSO_4(aq) \)[/tex] is Copper(II) sulfate, which is aqueous, meaning it is dissolved in water.
- [tex]\( 2 NaOH(aq) \)[/tex] is Sodium hydroxide, which is also aqueous, and it is a strong base.
2. Product Formation:
- [tex]\( Cu(OH)_2(s) \)[/tex] is Copper(II) hydroxide, which is a solid, indicating it precipitates out of the solution during the reaction.
- [tex]\( Na_2SO_4(aq) \)[/tex] is Sodium sulfate, which remains in the aqueous state, indicating it stays dissolved in the solution.
3. Reaction Analysis:
- Sodium hydroxide ([tex]\( NaOH \)[/tex]), being a base, reacts with the copper(II) sulfate ([tex]\( CuSO_4 \)[/tex]), which is a soluble metal salt.
- In this reaction, the [tex]\( Na^+ \)[/tex] ions from [tex]\( NaOH \)[/tex] combine with the [tex]\( SO_4^{2-} \)[/tex] ions from [tex]\( CuSO_4 \)[/tex] to form [tex]\( Na_2SO_4 \)[/tex], and the [tex]\( OH^- \)[/tex] ions from [tex]\( NaOH \)[/tex] combine with the [tex]\( Cu^{2+} \)[/tex] ions from [tex]\( CuSO_4 \)[/tex] to form [tex]\( Cu(OH)_2 \)[/tex], which precipitates out as a solid.
Therefore, analyzing the reaction, we see it demonstrates:
[tex]\[ \textbf{The ability of a base to react with a soluble metal salt.} \][/tex]
Hence, the correct answer is:
[tex]\[ \boxed{4} \][/tex]
This reaction specifically shows how a base, such as sodium hydroxide, interacts with a soluble metal salt like copper(II) sulfate, leading to the formation of an insoluble precipitate and a new soluble salt.
