Weak acid – strong base. A solution of a salt of a weak acid and a strong base will be basic.
For example, NaF is the salt of the strong base NaOH and the weak acid HF.
The conjugate acid of a strong base [OH^(-)] is weak (H_2O), but the conjugate base of a weak acid is strong. It will react with the water to produce hydroxide ions [OH^(-)].
F^(-) + H_2O ⇌ HF + OH^(-)
“Strong acid – strong base” is wrong. The solution will be neutral.
“Strong acid – weak base” is wrong. The solution will be acidic.
