To determine which of the given equations best represents a double replacement reaction, let's briefly review what each option represents and identify the correct one.
1. [tex]\(AB \rightarrow A + B\)[/tex]
- This reaction represents a decomposition reaction. In decomposition, a single compound breaks down into two or more simpler substances.
2. [tex]\(A + B \rightarrow AB\)[/tex]
- This reaction represents a synthesis reaction. In synthesis, two or more substances combine to form a single new compound.
3. [tex]\(A + BC \rightarrow AC + B\)[/tex]
- This reaction represents a single replacement reaction. In single replacement, one element replaces another element in a compound.
4. [tex]\(AC + BD \rightarrow AD + BC\)[/tex]
- This reaction represents a double replacement reaction. In double replacement, the positive ions (cations) and the negative ions (anions) of two different compounds switch places to form two new compounds.
Therefore, the equation [tex]\(AC + BD \rightarrow AD + BC\)[/tex] best represents a double replacement reaction.
So, the answer is:
[tex]\[ \boxed{4} \][/tex]
