Which of the following halides is most acidic?
Correct option is A. $$PCl_3$$
In $$CCl_4$$, carbon atom does not have $$d-$$ orbitals to accomodate a lone pair of electrons and hence is not a Lewis acid.
In $$PCl_3, SbCl_3$$ and $$BiCl_3$$ central atom has empty $$d-$$ orbitals in each case but electronegativity of $$P$$ is maximum, hence $$PCl_3$$ is strongest acid.
Option A is correct.