Step 1: Look at electron deficiency:
Beryllium in $\text{BeCl}_2$ has only 4 electrons around it, much less than an octet.
Step 2: Result:
This gap lets Be take lone pairs from donors, for example forming $[\text{BeCl}_4]^{2-}$ with $\text{Cl}^-$.
Ba, K and Li chlorides are ionic and stable, so they do not act as acceptors. Only $\text{BeCl}_2$ is a Lewis acid.
Final Answer:
The Lewis acid is $\text{BeCl}_2$, option (C).
\[ \boxed{\text{BeCl}_2} \]