The correct option is A CH4<NH3<H2O<HF
To predict their lewis acidities we shall evaluate the relative basicities of their conjugate bases, viz.CH−3,NH−2,OH−,F−
although size of central atom decreases from C to F, volume available to electron on the central atom decreases in he order: C,N,O,F
Thus the increasing basic character of these conjugate bases are CH−3>NH−2>OH−>F−
hence, order of increasing acidic strength is CH4<NH3<H2O<HF