Which describes the conjugate acid of NH3?

• A. NH4+
• B. NH2-
• C. NH3
• D. NH4OH

Answer: (A)

In acid-base chemistry, a conjugate acid forms when a base accepts a proton. Ammonia has a lone pair on nitrogen that can grab a proton, producing the ammonium ion, NH4+. That extra proton makes NH4+ the conjugate acid of NH3.

The other possibilities don’t fit this role. NH2- would come from removing a proton from NH3, not from adding one, so it’s not the conjugate acid. NH3 is the base itself, not its conjugate acid. NH4OH is a related species in solution representing NH4+ with OH-, but it is not the direct product of protonating NH3 in the context of conjugate acid–base pairs.