Electron deficient compounds are those where the central atom has less than 8 $e^{–}$ s in its outermost shell. Out of $BCl_3$ and $SiCl_4$, the former is an electron deficient compound since it has only 6 electrons in the outermost shell. $SiCl_4$ is not an electron deficient compound. However, it can accept electrons by expanding its octet due to presence of empty d-orbitals. Thus, it may form species like $SiF_6^{2–}$.