Step-by-step explanation:
The weakest conjugate base is option A) NO3-. According to the Bronsted-Lowry theory, a conjugate base is formed when an acid donates a proton. The strength of a conjugate base depends on the stability of the negative charge on the ion. The more stable the negative charge, the weaker the conjugate base. In this case, NO3- is a very stable ion because it is symmetrical and has a complete octet of electrons around each nitrogen and oxygen atom. Therefore, it forms the weakest conjugate base among the given options