The strength of a conjugate acid refers to its ability to donate a proton (H+) in a chemical reaction. The weaker the conjugate acid, the less likely it is to donate a proton. In this case, we are comparing the strength of conjugate acids based on the given options: a strong base, a weak acid, a strong acid, and a weak base.

To determine the weakest conjugate acid, we need to consider the strength of the corresponding base. The stronger the base, the weaker its conjugate acid will be.

Explanation:

a) A strong base:
A strong base is a substance that completely dissociates in water to produce hydroxide ions (OH-). Examples of strong bases include sodium hydroxide (NaOH) and potassium hydroxide (KOH). Since strong bases completely dissociate, they have a high concentration of hydroxide ions. As a result, their conjugate acids will be weak because hydroxide ions readily accept protons, making it less likely for them to donate a proton. Therefore, the weakest conjugate acid is associated with a strong base.

b) A weak acid:
A weak acid is a substance that only partially dissociates in water to produce hydrogen ions (H+). Examples of weak acids include acetic acid (CH3COOH) and formic acid (HCOOH). Weak acids have a limited ability to donate protons, so their conjugate acids will be stronger compared to a strong base.

c) A strong acid:
A strong acid is a substance that completely dissociates in water to produce hydrogen ions (H+). Examples of strong acids include hydrochloric acid (HCl) and sulfuric acid (H2SO4). Strong acids have a high concentration of hydrogen ions, so their conjugate acids will be weak.

d) A weak base:
A weak base is a substance that only partially accepts protons or donates electrons. Examples of weak bases include ammonia (NH3) and water (H2O). Weak bases have a limited ability to accept protons, so their conjugate acids will be stronger compared to a strong base.

Conclusion:
Based on the explanations above, the weakest conjugate acid is associated with a strong base (option A). Strong bases have a high concentration of hydroxide ions, making it less likely for them to donate protons and resulting in weaker conjugate acids.