Conjugate base for Brönsted acids H20 and HF are (3) OH– and F–, respectively 

Question : Conjugate base for Brönsted acids H2O and HF are –

(1) OH and H2F+, respectively

(2) H3O+ and F, respectively

(3) OH and F, respectively 

(4) H3O+ and H2F+, respectively

answer : from all above options the correct answer is “(3) OH and F, respectively ” Two substances that differ from each other only by one proton are referred to as a conjugate acid-base pair. Removing one H+ (both the atom and the charge) from both H2O and HF leaves OH- and F- ions respectively.
that is why we have marked option (3) for correct Answer.

Explanation of correct answer : you must know first the definition of Conjugate base , when a proton is removed from an acid then the Conjugate base is made or formed. in our question Brönsted acids H20 and HF are given and to remove proton from these acids we need some base named Conjugate base these needed bases are OH and F, respectively. hence we have given option 3 for correct answer as per question requirement.