Consider the following species $$CF_{4}, GeH_{4}, BCl_{3}, AlBr_{3}, H_{2}O, PH_{3}, PCl_{5}, CO_{2}, CH_{4}$$ and calculate value of $$(x - y)^{2} :$$
where, x : Total number of species which can act as only Lewis acid.
y : Total number of species which can act as Lewis acid as well as Lewis base.