SiCl4 has a vacant 3-d orbital however CCl4 does not. Because of this, SiCl4 acts a Lewis acid and is able to accept lone pair electrons.

Not Lewis Acid:

1. CCl4 (Carbon Tetrachloride)

Explanation:

1. BF3 (Boron Trifluoride):
Boron trifluoride (BF3) is a Lewis acid. It is a molecule with an empty p-orbital on the boron atom, which can accept a pair of electrons from a Lewis base. This makes it an electron pair acceptor and therefore a Lewis acid.

2. SnCl4 (Tin(IV) Chloride):
Tin(IV) chloride (SnCl4) is a Lewis acid. It has a central tin atom with four chlorine atoms bonded to it. The tin atom can accept a lone pair of electrons from a Lewis base, making it a Lewis acid.

3. CCl4 (Carbon Tetrachloride):
Carbon tetrachloride (CCl4) is not a Lewis acid. It consists of a central carbon atom bonded to four chlorine atoms. Carbon does not have an empty orbital available to accept electron pairs from a Lewis base, so it cannot act as a Lewis acid.

4. SF4 (Sulfur Tetrafluoride):
Sulfur tetrafluoride (SF4) is a Lewis acid. It has a central sulfur atom bonded to four fluorine atoms. The sulfur atom has an empty p-orbital that can accept a pair of electrons from a Lewis base, making it a Lewis acid.

In summary, among the given options, carbon tetrachloride (CCl4) is the only compound that is not a Lewis acid. It does not have an empty orbital available for accepting electron pairs from a Lewis base.

Ccl4