Final answer:
3) HNO₃ and NO₃⁻
The correct conjugate acid-base pair among the given options is HNO₃ and NO₃⁻, where HNO₃ is the conjugate acid that donates a proton to become NO₃⁻, the conjugate base.
Step-by-step explanation:
In the context of the Brønsted-Lowry acid-base theory, a conjugate acid-base pair consists of two species that transform into each other by the gain or loss of a proton (H+). When an acid donates a proton, the remaining species is its conjugate base, and when a base accepts a proton, it forms its conjugate acid.
Given the provided options, HNO₃ and NO₃⁻ form a conjugate acid-base pair. HNO₃ can donate a proton to become NO₃⁻, making HNO₃ the conjugate acid and NO₃⁻ the conjugate base. This aligns with the Brønsted-Lowry definition as one has an additional proton compared to the other.
Therefore, the correct answer to which of the following is a conjugate acid-base pair is option 3) HNO₃ and NO₃⁻.