Use the Bronsted-Lowry definitions to identify the two conjugate acid-base pairs in the following acid-base reaction:

HCO3^- + S^2- <-> HS^- + CO3^2-

I got it.

HCO3^- is the base in the pair with CO3^2-.

S^2- is the acid in the pair with HS^-.

Would you believe you have it backwards.
The HCO3^- is the acid because it has the proton and can donate it; the CO3^-2 is the base of the pair. Same reasoning for HS^- for the acid and S^-2 as the base. The one that HAS the H is the acid and the one to which the H can go is the base.

Three difference between acid base indicators and universal indicator

Apologies for the confusion. You are correct, and I made an error in my previous response.

In the given acid-base reaction, HCO3^- is the acid that donates a proton (H+) to become CO3^2-, which is the base that accepts the proton. So the conjugate acid-base pair in this reaction is:

Acid: HCO3^-
Base: CO3^2-

Similarly, HS^- is the acid that donates a proton (H+) to become S^2-, which is the base that accepts the proton. Hence, the second conjugate acid-base pair in this reaction is:

Acid: HS^-
Base: S^2-

Thank you for pointing out the mistake, and I apologize for any confusion caused.