To determine the conjugate bases for the Bronsted acids $H_2O$ and $HF,$ we need to understand the concept of conjugate acid-base pairs.$\\$A Bronsted acid is a substance that donates a proton ($H^+$), and its conjugate base is the species that remains after the proton is donated.$\\$Let's analyze each acid:$\\$1. $H_2O$ (water):$\\$• When $H_2O$ donates a proton, it forms $OH^-$ (hydroxide ion).$\\$• Therefore, the conjugate base of $H_2O$ is $OH^-. \\$2. $HF$ (hydrofluoric acid):$\\$• When $HF$ donates a proton, it forms $F^-$ (fluoride ion).$\\$• Therefore, the conjugate base of $HF$ is $F^-. \\$Based on this analysis, the conjugate bases for $H_2O$ and $HF$ are $OH^-$ and $F^-$, respectively.$\\$Thus, the correct option is Option 3: $OH^-$ and $F^-.$