Step 1: Sort the salts into three groups:
Basic (pH above 7): $\text{Na}_2\text{CO}_3$ and $\text{CH}_3\text{COONa}$, because the anions are conjugate bases of weak acids.
Neutral (pH about 7): $\text{NaNO}_3$, since neither ion hydrolyses.
Acidic (pH below 7): $\text{CuCl}_2$.
Step 2: Why CuCl2 is acidic:
The small, highly charged $\text{Cu}^{2+}$ ion pulls on water and releases protons:
$\text{Cu}^{2+} + 2\text{H}_2\text{O} \rightleftharpoons \text{Cu(OH)}_2 + 2\text{H}^+$.
$\text{Cl}^-$ is the conjugate base of a strong acid and does not hydrolyse.
Step 3: Answer:
Only $\text{CuCl}_2$ puts extra $\text{H}^+$ in the water, so its pH is the lowest.
Final Answer:
Option (B), $\text{CuCl}_2$.
\[ \boxed{\text{CuCl}_2 \text{ (B)}} \]