The strongest base amongst  ${\mathrm{OH}}^{-},{\mathrm{F}}^{-},{\mathrm{NH}}_2^{-}$ and ${\mathrm{CH}}_3^{-}$ is

The weakest acid amongst ${\mathrm{H}}_2\mathrm{O},\mathrm{HF},{\mathrm{NH}}_3$ and ${\mathrm{CH}}_4$is${\mathrm{CH}}_4$ . Hence, the strongest base will be ${\mathrm{CH}}_3^{-}$.  A strong base is one that totally ionizes in water and generates a lot of hydroxide ions. A base that produces a modest number of hydroxide ions when it is partly ionized in water is referred to as a weak base.